Changes for page 12 Validation and Transformation Language (VTL)

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From 7.5 to 7.4 From 9.1 to 8.1

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@@ -436,12 +436,12 @@
  Dataflow DF2(1.0.0) having the Dimensions TIME_PERIOD, INDICATOR, and COUNTRY and that such a programmer finds it convenient to calculate separately the parts of DF2(1.0.0) that have different combinations of values for INDICATOR and COUNTRY:
--* each part is calculated as a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] derived [[Data Set>>doc:xwiki:Glossary.Data set.WebHome]], result of a dedicated [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformation;{{footnote}}If the whole DF2(1.0) is calculated by means of just one VTL Transformation, then the mapping between the SDMX Dataflow and the corresponding VTL dataset is one-to-one and this kind of mapping (one SDMX Dataflow to many VTL datasets) does not apply.{{/footnote}}
--* the data structure of all these [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[Data Sets>>doc:xwiki:Glossary.Data set.WebHome]] has the TIME_PERIOD identifier and does not have the INDICATOR and COUNTRY identifiers.{{footnote}}This is possible as each VTL dataset corresponds to one particular combination of values of INDICATOR and COUNTRY.{{/footnote}}
++* each part is calculated as a VTL derived Data Set, result of a dedicated VTL Transformation;{{footnote}}If the whole DF2(1.0) is calculated by means of just one VTL Transformation, then the mapping between the SDMX Dataflow and the corresponding VTL dataset is one-to-one and this kind of mapping (one SDMX Dataflow to many VTL datasets) does not apply.{{/footnote}}
++* the data structure of all these VTL Data Sets has the TIME_PERIOD identifier and does not have the INDICATOR and COUNTRY identifiers.{{footnote}}This is possible as each VTL dataset corresponds to one particular combination of values of INDICATOR and COUNTRY.{{/footnote}}
--Under these hypothesis, such derived [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[Data Sets>>doc:xwiki:Glossary.Data set.WebHome]] can be (% style="color:#2ecc71" %)mapped(%%) to DF2(1.0.0) by declaring the DimensionComponents INDICATOR and COUNTRY as mapping dimensions{{footnote}}The mapping dimensions are defined as FromVtlSpaceKeys of the FromVtlSuperSpace of the VtlDataflowMapping relevant to DF2(1.0).{{/footnote}}.
++Under these hypothesis, such derived VTL Data Sets can be mapped to DF2(1.0.0) by declaring the DimensionComponents INDICATOR and COUNTRY as mapping dimensions{{footnote}}The mapping dimensions are defined as FromVtlSpaceKeys of the FromVtlSuperSpace of the VtlDataflowMapping relevant to DF2(1.0).{{/footnote}}.
--The corresponding [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformations, assuming that the result needs to be persistent, would be of this kind:{{footnote}}the symbol of the VTL persistent assignment is used (<-){{/footnote}}
++The corresponding VTL Transformations, assuming that the result needs to be persistent, would be of this kind:{{footnote}}the symbol of the VTL persistent assignment is used (<-){{/footnote}}
  ‘DF2(1.0.0)/INDICATORvalue.COUNTRYvalue’ <- expression
@@ -451,72 +451,74 @@
  [[image:1747388206717-256.png]]
--As said, it is assumed that these [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] derived [[Data Sets>>doc:xwiki:Glossary.Data set.WebHome]] have the TIME_PERIOD as the only identifier. In the mapping from [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to SMDX, the [[Dimensions>>doc:xwiki:Glossary.Dimension.WebHome]] INDICATOR and COUNTRY are added to the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] data structure on order to obtain the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] one, with the following values respectively:
++As said, it is assumed that these VTL derived Data Sets have the TIME_PERIOD as the only identifier. In the mapping from VTL to SMDX, the Dimensions INDICATOR and COUNTRY are added to the VTL data structure on order to obtain the SDMX one, with the following values respectively:
  [[image:1747388148322-387.png]]
--It should be noted that the application of this many-to-one mapping from [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] is equivalent to an appropriate sequence of [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformations. These use the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] operator “calc” to add the proper [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] identifiers (in the example, INDICATOR and COUNTRY) and to assign to them the proper values and the operator “union” in order to obtain the final [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[dataset>>doc:xwiki:Glossary.Data set.WebHome]] (in the example DF2(1.0.0)), that can be (% style="color:#2ecc71" %)mapped(%%) one-to-one to the homonymous [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[Dataflow>>doc:xwiki:Glossary.Dataflow.WebHome]]. Following the same example, these [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformations would be:
++It should be noted that the application of this many-to-one mapping from VTL to SDMX is equivalent to an appropriate sequence of VTL Transformations. These use the VTL operator “calc” to add the proper VTL identifiers (in the example, INDICATOR and COUNTRY) and to assign to them the proper values and the operator “union” in order to obtain the final VTL dataset (in the example DF2(1.0.0)), that can be mapped oneto-one to the homonymous SDMX Dataflow. Following the same example, these VTL Transformations would be:
  [[image:1747388179021-814.png]]
--In other words, starting from the [[datasets>>doc:xwiki:Glossary.Data set.WebHome]] explicitly calculated through [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] (in the example ‘DF2(1.0)/GDPPERCAPITA.USA’ and so on), the first step consists in calculating other (non-persistent) [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[datasets>>doc:xwiki:Glossary.Data set.WebHome]] (in the example DF2bis_GDPPERCAPITA_USA and so on) by adding the identifiers INDICATOR and COUNTRY with the desired values (//INDICATORvalue// and //COUNTRYvalue)//. Finally, all these non-persistent [[Data Sets>>doc:xwiki:Glossary.Data set.WebHome]] are united and give the final result DF2(1.0){{footnote}}The result is persistent in this example but it can be also non persistent if needed.{{/footnote}}, which can be (% style="color:#2ecc71" %)mapped(%%) one-to-one to the homonymous [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[Dataflow>>doc:xwiki:Glossary.Dataflow.WebHome]] having the [[dimension>>doc:xwiki:Glossary.Dimension.WebHome]] [[components>>doc:xwiki:Glossary.Component.WebHome]] TIME_PERIOD, INDICATOR and COUNTRY.
++In other words, starting from the datasets explicitly calculated through VTL (in the example ‘DF2(1.0)/GDPPERCAPITA.USA’ and so on), the first step consists in calculating other (non-persistent) VTL datasets (in the example
--Therefore, (% style="color:#2ecc71" %)mapping(%%) different [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[datasets>>doc:xwiki:Glossary.Data set.WebHome]] having the same data structure to different parts of a [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[Dataflow>>doc:xwiki:Glossary.Dataflow.WebHome]], i.e. in the direction from [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], through the ordered concatenation notation is equivalent to a proper use of the operators “calc” and “union” on such [[datasets>>doc:xwiki:Glossary.Data set.WebHome]].{{footnote}}In case the ordered concatenation notation from VTL to SDMX is used, the set of Transformations described above is implicitly performed; therefore, in order to test the overall compliance of the VTL program to the VTL consistency rules, these implicit Transformations have to be considered as part of the VTL program even if they are not explicitly coded.{{/footnote}}
++DF2bis_GDPPERCAPITA_USA and so on) by adding the identifiers INDICATOR and COUNTRY with the desired values (//INDICATORvalue// and //COUNTRYvalue)//. Finally, all these non-persistent Data Sets are united and give the final result DF2(1.0){{footnote}}The result is persistent in this example but it can be also non persistent if needed.{{/footnote}}, which can be mapped one-to-one to the homonymous SDMX Dataflow having the dimension components TIME_PERIOD, INDICATOR and COUNTRY.
--It is worth noting that in the direction from [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] it is mandatory to specify the value for every [[Dimension>>doc:xwiki:Glossary.Dimension.WebHome]] on which the (% style="color:#2ecc71" %)mapping(%%) is based (in other word, in the name of the calculated [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[dataset>>doc:xwiki:Glossary.Data set.WebHome]] is __not__ possible to omit the value of some of the Dimensions).
++Therefore, mapping different VTL datasets having the same data structure to different parts of a SDMX Dataflow, i.e. in the direction from VTL to SDMX, through the ordered concatenation notation is equivalent to a proper use of the operators “calc” and “union” on such datasets.{{footnote}}In case the ordered concatenation notation from VTL to SDMX is used, the set of Transformations described above is implicitly performed; therefore, in order to test the overall compliance of the VTL program to the VTL consistency rules, these implicit Transformations have to be considered as part of the VTL program even if they are not explicitly coded.{{/footnote}}
++It is worth noting that in the direction from VTL to SDMX it is mandatory to specify the value for every Dimension on which the mapping is based (in other word, in the name of the calculated VTL dataset is __not__ possible to omit the value of some of the Dimensions).
++
  === 12.3.7 Mapping variables and value domains between VTL and SDMX ===
--With reference to the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] “model for Variables and Value domains”, the following additional mappings have to be considered:
++With reference to the VTL “model for Variables and Value domains”, the following additional mappings have to be considered:
  (% style="width:895.294px" %)
  |(% style="width:278px" %)**VTL**|(% style="width:613px" %)**SDMX**
--|(% style="width:278px" %)**[[Data Set>>doc:xwiki:Glossary.Data set.WebHome]] [[Component>>doc:xwiki:Glossary.Component.WebHome]]**|(% style="width:613px" %)Although this abstraction exists in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], it does not have an explicit definition and correspond to a [[Component>>doc:xwiki:Glossary.Component.WebHome]] (either a DimensionComponent or a [[Measure>>doc:xwiki:Glossary.Measure.WebHome]] or a DataAttribute) belonging to one specific [[Dataflow>>doc:xwiki:Glossary.Dataflow.WebHome]]{{footnote}}Through SDMX Constraints, it is possible to specify the values that a Component of a Dataflow can assume.{{/footnote}}
++|(% style="width:278px" %)**Data Set Component**|(% style="width:613px" %)Although this abstraction exists in SDMX, it does not have an explicit definition and correspond to a Component (either a DimensionComponent or a Measure or a DataAttribute) belonging to one specific Dataflow{{footnote}}Through SDMX Constraints, it is possible to specify the values that a Component of a Dataflow can assume.{{/footnote}}
  |(% style="width:278px" %)**Represented Variable**|(% style="width:613px" %)(((
--(% style="color:#2ecc71" %)**Concept**(%%) with a definite
++**Concept** with a definite
--[[Representation>>doc:xwiki:Glossary.Representation.WebHome]]
++Representation
  )))
  |(% style="width:278px" %)**Value Domain**|(% style="width:613px" %)(((
--**[[Representation>>doc:xwiki:Glossary.Representation.WebHome]]** (see the Structure Pattern in the Base Package)
++**Representation** (see the Structure Pattern in the Base Package)
  )))
  |(% style="width:278px" %)**Enumerated Value Domain /
--[[Code>>doc:xwiki:Glossary.Code.WebHome]] List**|(% style="width:613px" %)**Codelist**
--|(% style="width:278px" %)**[[Code>>doc:xwiki:Glossary.Code.WebHome]]**|(% style="width:613px" %)(((
--**[[Code>>doc:xwiki:Glossary.Code.WebHome]]** (for enumerated DimensionComponent, [[Measure>>doc:xwiki:Glossary.Measure.WebHome]], DataAttribute)
++Code List**|(% style="width:613px" %)**Codelist**
++|(% style="width:278px" %)**Code**|(% style="width:613px" %)(((
++**Code** (for enumerated DimensionComponent, Measure, DataAttribute)
  )))
  |(% style="width:278px" %)**Described Value Domain**|(% style="width:613px" %)(((
--non-enumerated** [[Representation>>doc:xwiki:Glossary.Representation.WebHome]] **(having [[Facets>>doc:xwiki:Glossary.Facet.WebHome]] / ExtendedFacets, see the Structure Pattern in the Base Package)
++non-enumerated** Representation **(having Facets / ExtendedFacets, see the Structure Pattern in the Base Package)
  )))
--|(% style="width:278px" %)**Value**|(% style="width:613px" %)Although this abstraction exists in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], it does not have an explicit definition and correspond to a **[[Code>>doc:xwiki:Glossary.Code.WebHome]]** of a Codelist (for enumerated [[Representations>>doc:xwiki:Glossary.Representation.WebHome]]) or to a valid **value **(for non-enumerated** **[[Representations>>doc:xwiki:Glossary.Representation.WebHome]])
--|(% style="width:278px" %)**Value Domain Subset / Set**|(% style="width:613px" %)This abstraction does not exist in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]
--|(% style="width:278px" %)**Enumerated Value Domain Subset / Enumerated Set**|(% style="width:613px" %)This abstraction does not exist in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]
--|(% style="width:278px" %)**Described Value Domain Subset / Described Set**|(% style="width:613px" %)This abstraction does not exist in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]
--|(% style="width:278px" %)**Set list**|(% style="width:613px" %)This abstraction does not exist in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]
++|(% style="width:278px" %)**Value**|(% style="width:613px" %)Although this abstraction exists in SDMX, it does not have an explicit definition and correspond to a **Code** of a Codelist (for enumerated Representations) or to a valid **value **(for non-enumerated** **Representations)
++|(% style="width:278px" %)**Value Domain Subset / Set**|(% style="width:613px" %)This abstraction does not exist in SDMX
++|(% style="width:278px" %)**Enumerated Value Domain Subset / Enumerated Set**|(% style="width:613px" %)This abstraction does not exist in SDMX
++|(% style="width:278px" %)**Described Value Domain Subset / Described Set**|(% style="width:613px" %)This abstraction does not exist in SDMX
++|(% style="width:278px" %)**Set list**|(% style="width:613px" %)This abstraction does not exist in SDMX
--The main difference between [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] and [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] relies on the fact that the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[artefacts>>doc:xwiki:Glossary.Artefact.WebHome]] for defining subsets of Value Domains do not exist in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], therefore the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] features for referring to predefined subsets are not available in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]. These [[artefacts>>doc:xwiki:Glossary.Artefact.WebHome]] are the Value Domain Subset (or Set), either enumerated or described, the Set List (list of values belonging to enumerated subsets) and the [[Data Set>>doc:xwiki:Glossary.Data set.WebHome]] [[Component>>doc:xwiki:Glossary.Component.WebHome]] (aimed at defining the set of values that the [[Component>>doc:xwiki:Glossary.Component.WebHome]] of a [[Data Set>>doc:xwiki:Glossary.Data set.WebHome]] can take, possibly a subset of the [[codes>>doc:xwiki:Glossary.Code.WebHome]] of Value Domain).
++The main difference between VTL and SDMX relies on the fact that the VTL artefacts for defining subsets of Value Domains do not exist in SDMX, therefore the VTL features for referring to predefined subsets are not available in SDMX. These artefacts are the Value Domain Subset (or Set), either enumerated or described, the Set List (list of values belonging to enumerated subsets) and the Data Set Component (aimed at defining the set of values that the Component of a Data Set can take, possibly a subset of the codes of Value Domain).
--Another difference consists in the fact that all Value Domains are considered as identifiable objects in [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] either if enumerated or not, while in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] the Codelist (corresponding to a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] enumerated Value Domain) is identifiable, while the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] non-enumerated [[Representation>>doc:xwiki:Glossary.Representation.WebHome]] (corresponding to a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] non-enumerated Value Domain) is not identifiable. As a consequence, the definition of the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Rulesets, which in [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] can refer either to enumerated or non-enumerated value domains, in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] can refer only to enumerated Value Domains (i.e. to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] Codelists). As for the (% style="color:#2ecc71" %)mapping(%%) between [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] variables and [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] (% style="color:#2ecc71" %)Concepts(%%), it should be noted that these [[artefacts>>doc:xwiki:Glossary.Artefact.WebHome]] do not coincide perfectly. In fact, the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] variables are represented variables, defined always on the same Value Domain (“[[Representation>>doc:xwiki:Glossary.Representation.WebHome]]” in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]) independently of the [[data set>>doc:xwiki:Glossary.Data set.WebHome]] / data structure in which they appear{{footnote}}By using represented variables, VTL can assume that data structures having the same variables as identifiers can be composed one another because the correspondent values can match.{{/footnote}}, while the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] (% style="color:#2ecc71" %)Concepts(%%) can have different [[Representations>>doc:xwiki:Glossary.Representation.WebHome]] in different DataStructures.{{footnote}}A Concept becomes a Component in a DataStructureDefinition, and Components can have different LocalRepresentations in different DataStructureDefinitions, also overriding the (possible) base representation of the Concept.{{/footnote}} This means that one [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] (% style="color:#2ecc71" %)Concept(%%) can correspond to many [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Variables, one for each [[representation>>doc:xwiki:Glossary.Representation.WebHome]] the (% style="color:#2ecc71" %)Concept(%%) has.
++Another difference consists in the fact that all Value Domains are considered as identifiable objects in VTL either if enumerated or not, while in SDMX the Codelist (corresponding to a VTL enumerated Value Domain) is identifiable, while the SDMX non-enumerated Representation (corresponding to a VTL non-enumerated Value Domain) is not identifiable. As a consequence, the definition of the VTL Rulesets, which in VTL can refer either to enumerated or non-enumerated value domains, in SDMX can refer only to enumerated Value Domains (i.e. to SDMX Codelists). As for the mapping between VTL variables and SDMX Concepts, it should be noted that these artefacts do not coincide perfectly. In fact, the VTL variables are represented variables, defined always on the same Value Domain (“Representation” in SDMX) independently of the data set / data structure in which they appear{{footnote}}By using represented variables, VTL can assume that data structures having the same variables as identifiers can be composed one another because the correspondent values can match.{{/footnote}}, while the SDMX Concepts can have different Representations in different DataStructures.{{footnote}}A Concept becomes a Component in a DataStructureDefinition, and Components can have different LocalRepresentations in different DataStructureDefinitions, also overriding the (possible) base representation of the Concept.{{/footnote}} This means that one SDMX Concept can correspond to many VTL Variables, one for each representation the Concept has.
--Therefore, it is important to be aware that some [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] operations (for example the binary operations at [[data set>>doc:xwiki:Glossary.Data set.WebHome]] (% style="color:#2ecc71" %)level(%%)) are consistent only if the [[components>>doc:xwiki:Glossary.Component.WebHome]] having the same names in the operated [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[Data Sets>>doc:xwiki:Glossary.Data set.WebHome]] have also the same [[representation>>doc:xwiki:Glossary.Representation.WebHome]] (i.e. the same Value Domain as for [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]]). For example, it is possible to obtain correct results from the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] expression
++Therefore, it is important to be aware that some VTL operations (for example the binary operations at data set level) are consistent only if the components having the same names in the operated VTL Data Sets have also the same representation (i.e. the same Value Domain as for VTL). For example, it is possible to obtain correct results from the VTL expression
--DS_c := DS_a + DS_b (where DS_a, DS_b, DS_c are [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[Data Sets>>doc:xwiki:Glossary.Data set.WebHome]])
++DS_c := DS_a + DS_b (where DS_a, DS_b, DS_c are VTL Data Sets)
--if the matching [[components>>doc:xwiki:Glossary.Component.WebHome]] in DS_a and DS_b (e.g. ref_date, geo_area, sector …) refer to the same general [[representation>>doc:xwiki:Glossary.Representation.WebHome]]. In simpler words, DS_a and DS_b must use the same values/[[codes>>doc:xwiki:Glossary.Code.WebHome]] (for ref_date, geo_area, sector … ), otherwise the relevant values would not match and the result of the operation would be wrong.
++if the matching components in DS_a and DS_b (e.g. ref_date, geo_area, sector …) refer to the same general representation. In simpler words, DS_a and DS_b must use the same values/codes (for ref_date, geo_area, sector … ), otherwise the relevant values would not match and the result of the operation would be wrong.
--As mentioned, the property above is not enforced by construction in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], and different [[representations>>doc:xwiki:Glossary.Representation.WebHome]] of the same (% style="color:#2ecc71" %)Concept(%%) can be not compatible one another (for example, it may happen that geo_area is represented by ISO-alpha-3 [[codes>>doc:xwiki:Glossary.Code.WebHome]] in DS_a and by ISO alpha-2 [[codes>>doc:xwiki:Glossary.Code.WebHome]] in DS_b). Therefore, it will be up to the definer of [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]]
++As mentioned, the property above is not enforced by construction in SDMX, and different representations of the same Concept can be not compatible one another (for example, it may happen that geo_area is represented by ISO-alpha-3 codes in DS_a and by ISO alpha-2 codes in DS_b). Therefore, it will be up to the definer of VTL
--Transformations to ensure that the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] expressions are consistent with the actual [[representations>>doc:xwiki:Glossary.Representation.WebHome]] of the correspondent [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] (% style="color:#2ecc71" %)Concepts(%%).
++Transformations to ensure that the VTL expressions are consistent with the actual representations of the correspondent SDMX Concepts.
--It remains up to the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]-[[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] definer also the assurance of the consistency between a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Ruleset defined on Variables and the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[Components>>doc:xwiki:Glossary.Component.WebHome]] on which the Ruleset is applied. In fact, a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Ruleset is expressed by means of the values of the Variables (i.e. [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] (% style="color:#2ecc71" %)Concepts(%%)), i.e. assuming definite [[representations>>doc:xwiki:Glossary.Representation.WebHome]] for them (e.g. ISOalpha-3 for country). If the Ruleset is applied to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[Components>>doc:xwiki:Glossary.Component.WebHome]] that have the same name of the (% style="color:#2ecc71" %)Concept(%%) they refer to but different [[representations>>doc:xwiki:Glossary.Representation.WebHome]] (e.g. ISO-alpha-2 for country), the Ruleset cannot work properly.
++It remains up to the SDMX-VTL definer also the assurance of the consistency between a VTL Ruleset defined on Variables and the SDMX Components on which the Ruleset is applied. In fact, a VTL Ruleset is expressed by means of the values of the Variables (i.e. SDMX Concepts), i.e. assuming definite representations for them (e.g. ISOalpha-3 for country). If the Ruleset is applied to SDMX Components that have the same name of the Concept they refer to but different representations (e.g. ISO-alpha-2 for country), the Ruleset cannot work properly.
  == 12.4 Mapping between SDMX and VTL Data Types ==
  === 12.4.1 VTL Data types ===
--According to the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] User Guide the possible operations in [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] depend on the data types of the [[artefacts>>doc:xwiki:Glossary.Artefact.WebHome]]. For example, numbers can be multiplied but text strings cannot. In the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformations, the compliance between the operators and the data types of their operands is statically checked, i.e., violations result in compile-time errors.
++According to the VTL User Guide the possible operations in VTL depend on the data types of the artefacts. For example, numbers can be multiplied but text strings cannot. In the VTL Transformations, the compliance between the operators and the data types of their operands is statically checked, i.e., violations result in compile-time errors.
--The [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] data types are sub-divided in scalar types (like integers, strings, etc.), which are the types of the scalar values, and compound types (like [[Data Sets>>doc:xwiki:Glossary.Data set.WebHome]], [[Components>>doc:xwiki:Glossary.Component.WebHome]], Rulesets, etc.), which are the types of the compound structures. See below the diagram of the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] data types, taken from the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] User Manual:
++The VTL data types are sub-divided in scalar types (like integers, strings, etc.), which are the types of the scalar values, and compound types (like Data Sets, Components, Rulesets, etc.), which are the types of the compound structures. See below the diagram of the VTL data types, taken from the VTL User Manual:
  [[image:1747388434672-948.png]]
@@ -523,9 +523,9 @@
  (% class="wikigeneratedid" id="HFigure222013VTLDataTypes" %)
  **Figure 22 – VTL Data Types**
--The [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] scalar types are in turn subdivided in basic scalar types, which are elementary (not defined in term of other data types) and Value Domain and Set scalar types, which are defined in terms of the basic scalar types.
++The VTL scalar types are in turn subdivided in basic scalar types, which are elementary (not defined in term of other data types) and Value Domain and Set scalar types, which are defined in terms of the basic scalar types.
--The [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar types are listed below and follow a hierarchical structure in terms of supersets/subsets (e.g. "scalar" is the superset of all the basic scalar types):
++The VTL basic scalar types are listed below and follow a hierarchical structure in terms of supersets/subsets (e.g. "scalar" is the superset of all the basic scalar types):
  [[image:1747388465321-274.png]]
@@ -533,25 +533,25 @@
  === 12.4.2 VTL basic scalar types and SDMX data types ===
--The [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] assumes that a basic scalar type has a unique internal [[representation>>doc:xwiki:Glossary.Representation.WebHome]] and can have more external [[representations>>doc:xwiki:Glossary.Representation.WebHome]].
++The VTL assumes that a basic scalar type has a unique internal representation and can have more external representations.
--The internal [[representation>>doc:xwiki:Glossary.Representation.WebHome]] is the format used within a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] system to represent (and process) all the scalar values of a certain type. In principle, this format is hidden and not necessarily known by users. The external [[representations>>doc:xwiki:Glossary.Representation.WebHome]] are instead the external formats of the values of a certain basic scalar type, i.e. the formats known by the users. For example, the internal [[representation>>doc:xwiki:Glossary.Representation.WebHome]] of the dates can be an integer counting the days since a predefined date (e.g. from 01/01/4713 BC up to 31/12/5874897 AD like in Postgres) while two possible external [[representations>>doc:xwiki:Glossary.Representation.WebHome]] are the formats YYYY-MMGG and MM-GG-YYYY (e.g. respectively 2010-12-31 and 12-31-2010).
++The internal representation is the format used within a VTL system to represent (and process) all the scalar values of a certain type. In principle, this format is hidden and not necessarily known by users. The external representations are instead the external formats of the values of a certain basic scalar type, i.e. the formats known by the users. For example, the internal representation of the dates can be an integer counting the days since a predefined date (e.g. from 01/01/4713 BC up to 31/12/5874897 AD like in Postgres) while two possible external representations are the formats YYYY-MMGG and MM-GG-YYYY (e.g. respectively 2010-12-31 and 12-31-2010).
--The internal [[representation>>doc:xwiki:Glossary.Representation.WebHome]] is the reference format that allows [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to operate on more values of the same type (for example on more dates) even if such values have different external formats: these values are all converted to the unique internal [[representation>>doc:xwiki:Glossary.Representation.WebHome]] so that they can be composed together (e.g. to find the more recent date, to find the time span between these dates and so on).
++The internal representation is the reference format that allows VTL to operate on more values of the same type (for example on more dates) even if such values have different external formats: these values are all converted to the unique internal representation so that they can be composed together (e.g. to find the more recent date, to find the time span between these dates and so on).
--The [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] assumes that a unique internal [[representation>>doc:xwiki:Glossary.Representation.WebHome]] exists for each basic scalar type but does not prescribe any particular format for it, leaving the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] systems free to using they preferred or already existing internal format. By consequence, in [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] the basic scalar types are abstractions not associated to a specific format.
++The VTL assumes that a unique internal representation exists for each basic scalar type but does not prescribe any particular format for it, leaving the VTL systems free to using they preferred or already existing internal format. By consequence, in VTL the basic scalar types are abstractions not associated to a specific format.
--[[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] data types are conceived instead to support the data exchange, therefore they do have a format, which is known by the users and correspond, in [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] terms, to external [[representations>>doc:xwiki:Glossary.Representation.WebHome]]. Therefore, for each [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar type there can be more [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] data types (the latter are explained in the section "General Notes for Implementers" of this document and are actually much more numerous than the former).
++SDMX data types are conceived instead to support the data exchange, therefore they do have a format, which is known by the users and correspond, in VTL terms, to external representations. Therefore, for each VTL basic scalar type there can be more SDMX data types (the latter are explained in the section "General Notes for Implementers" of this document and are actually much more numerous than the former).
--The following paragraphs describe the mapping between the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] data types and the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar types. This mapping shall be presented in the two directions of possible conversion, i.e. from [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] to [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] and vice-versa.
++The following paragraphs describe the mapping between the SDMX data types and the VTL basic scalar types. This mapping shall be presented in the two directions of possible conversion, i.e. from SDMX to VTL and vice-versa.
--The conversion from [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] to [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] happens when an [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[artefact>>doc:xwiki:Glossary.Artefact.WebHome]] acts as inputs of a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformation. As already said, in fact, at compile time the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] needs to know the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] type of the operands in order to check their compliance with the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] operators and at runtime it must convert the values from their external ([[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]) [[representations>>doc:xwiki:Glossary.Representation.WebHome]] to the corresponding internal ([[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]]) ones.
++The conversion from SDMX to VTL happens when an SDMX artefact acts as inputs of a VTL Transformation. As already said, in fact, at compile time the VTL needs to know the VTL type of the operands in order to check their compliance with the VTL operators and at runtime it must convert the values from their external (SDMX) representations to the corresponding internal (VTL) ones.
--The opposite conversion, i.e. from [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], happens when a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] result, i.e. a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] [[Data Set>>doc:xwiki:Glossary.Data set.WebHome]] output of a Transformation, must become a [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[artefact>>doc:xwiki:Glossary.Artefact.WebHome]] (or part of it). The values of the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] result must be converted into the desired ([[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]) external [[representations>>doc:xwiki:Glossary.Representation.WebHome]] (data types) of the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[artefact>>doc:xwiki:Glossary.Artefact.WebHome]].
++The opposite conversion, i.e. from VTL to SDMX, happens when a VTL result, i.e. a VTL Data Set output of a Transformation, must become a SDMX artefact (or part of it). The values of the VTL result must be converted into the desired (SDMX) external representations (data types) of the SDMX artefact.
  === 12.4.3 Mapping SDMX data types to VTL basic scalar types ===
--The following table describes the default mapping for converting from the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] data types to the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar types.
++The following table describes the default mapping for converting from the SDMX data types to the VTL basic scalar types.
  (% style="width:823.294px" %)
  |(% style="width:509px" %)**SDMX data type (BasicComponentDataType)**|(% style="width:312px" %)**Default VTL basic scalar type**
@@ -587,7 +587,7 @@
  Short
  (corresponds to XML Schema xs:short datatype; between -32768 and -32767 (inclusive))
  )))|(% style="width:312px" %)integer
--|(% style="width:509px" %)[[Decimal>>doc:xwiki:Glossary.Decimals.WebHome]] (corresponds to XML Schema xs:decimal datatype; subset of real numbers that can be represented as [[decimals>>doc:xwiki:Glossary.Decimals.WebHome]])|(% style="width:312px" %)number
++|(% style="width:509px" %)Decimal (corresponds to XML Schema xs:decimal datatype; subset of real numbers that can be represented as decimals)|(% style="width:312px" %)number
  |(% style="width:509px" %)(((
  Float
  (corresponds to XML Schema xs:float datatype; patterned after the IEEE single-precision 32-bit floating point type)
@@ -598,7 +598,7 @@
  )))|(% style="width:312px" %)number
  |(% style="width:509px" %)(((
  Boolean
--(corresponds to the XML Schema xs:boolean datatype; support the mathematical (% style="color:#2ecc71" %)concept(%%) of binary-valued logic: {true, false})
++(corresponds to the XML Schema xs:boolean datatype; support the mathematical concept of binary-valued logic: {true, false})
  )))|(% style="width:312px" %)boolean
  (% style="width:822.294px" %)
@@ -612,15 +612,15 @@
  )))|(% colspan="1" style="width:311px" %)integer
  |(% colspan="2" style="width:507px" %)(((
  InclusiveValueRange
--([[decimal>>doc:xwiki:Glossary.Decimals.WebHome]] number within a closed interval, whose bounds are specified in the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[representation>>doc:xwiki:Glossary.Representation.WebHome]] by the [[facets>>doc:xwiki:Glossary.Facet.WebHome]] minValue and maxValue)
++(decimal number within a closed interval, whose bounds are specified in the SDMX representation by the facets minValue and maxValue)
  )))|(% colspan="1" style="width:311px" %)number
  |(% colspan="2" style="width:507px" %)(((
  ExclusiveValueRange
--([[decimal>>doc:xwiki:Glossary.Decimals.WebHome]] number within an open interval, whose bounds are specified in the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[representation>>doc:xwiki:Glossary.Representation.WebHome]] by the [[facets>>doc:xwiki:Glossary.Facet.WebHome]] minValue and maxValue)
++(decimal number within an open interval, whose bounds are specified in the SDMX representation by the facets minValue and maxValue)
  )))|(% colspan="1" style="width:311px" %)number
  |(% colspan="2" style="width:507px" %)(((
  Incremental
--([[decimal>>doc:xwiki:Glossary.Decimals.WebHome]] number the increased by a specific interval (defined by the interval [[facet>>doc:xwiki:Glossary.Facet.WebHome]]), which is typically enforced outside of the XML validation)
++(decimal number the increased by a specific interval (defined by the interval facet), which is typically enforced outside of the XML validation)
  )))|(% colspan="1" style="width:311px" %)number
  |(% colspan="2" style="width:507px" %)(((
  ObservationalTimePeriod
@@ -677,19 +677,19 @@
  )))|(% colspan="2" style="width:312px" %)date
  |(% colspan="1" style="width:507px" %)(((
  TimeRange
--(YYYY-MM-DD(Thh:mm:ss)?/)
++(YYYY-MM-DD(Thh:mm:ss)?/<duration>)
  )))|(% colspan="2" style="width:312px" %)time
  |(% colspan="1" style="width:507px" %)(((
  Month
--(MM; speicifies a month independent of a year; e.g. February is black history month in the United States)
++(~-~-MM; speicifies a month independent of a year; e.g. February is black history month in the United States)
  )))|(% colspan="2" style="width:312px" %)string
  |(% colspan="1" style="width:507px" %)(((
  MonthDay
--(MM-DD; specifies a day within a month independent of a year; e.g. Christmas is December 25^^th^^; used to specify reporting year start day)
++(~-~-MM-DD; specifies a day within a month independent of a year; e.g. Christmas is December 25^^th^^; used to specify reporting year start day)
  )))|(% colspan="2" style="width:312px" %)string
  |(% colspan="1" style="width:507px" %)(((
  Day
--(-DD; specifies a day independent of a month or year; e.g. the 15^^th^^ is payday)
++(~-~--DD; specifies a day independent of a month or year; e.g. the 15^^th^^ is payday)
  )))|(% colspan="2" style="width:312px" %)string
  |(% colspan="1" style="width:507px" %)(((
  Time
@@ -707,11 +707,11 @@
  (% class="wikigeneratedid" id="HFigure142013MappingsfromSDMXdatatypestoVTLBasicScalarTypes" %)
  **Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types**
--When [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] takes in input [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[artefacts>>doc:xwiki:Glossary.Artefact.WebHome]], it is assumed that a type conversion according to the table above always happens. In case a different [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar type is desired, it can be achieved in the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] program taking in input the default [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar type above and applying to it the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] type conversion features (see the implicit and explicit type conversion and the "cast" operator in the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Reference Manual).
++When VTL takes in input SDMX artefacts, it is assumed that a type conversion according to the table above always happens. In case a different VTL basic scalar type is desired, it can be achieved in the VTL program taking in input the default VTL basic scalar type above and applying to it the VTL type conversion features (see the implicit and explicit type conversion and the "cast" operator in the VTL Reference Manual).
  === 12.4.4 Mapping VTL basic scalar types to SDMX data types ===
--The following table describes the default conversion from the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar types to the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] data types .
++The following table describes the default conversion from the VTL basic scalar types to the SDMX data types .
  (% style="width:1073.29px" %)
  |(% style="width:207px" %)(((
@@ -723,13 +723,13 @@
  |(% style="width:207px" %)Number|(% style="width:462px" %)Float|(% style="width:402px" %)Like XML (xs:float)
  |(% style="width:207px" %)Integer|(% style="width:462px" %)Integer|(% style="width:402px" %)Like XML (xs:int)
  |(% style="width:207px" %)Date|(% style="width:462px" %)DateTime|(% style="width:402px" %)YYYY-MM-DDT00:00:00Z
--|(% style="width:207px" %)Time|(% style="width:462px" %)StandardTimePeriod|(% style="width:402px" %)/ (as defined above)
++|(% style="width:207px" %)Time|(% style="width:462px" %)StandardTimePeriod|(% style="width:402px" %)<date>/<date> (as defined above)
  |(% style="width:207px" %)time_period|(% style="width:462px" %)(((
  ReportingTimePeriod
  (StandardReportingPeriod)
  )))|(% style="width:402px" %)(((
  YYYY-Pppp
--(according to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] )
++(according to SDMX )
  )))
  |(% style="width:207px" %)Duration|(% style="width:462px" %)Duration|(% style="width:402px" %)(((
  Like XML (xs:duration)
@@ -740,9 +740,9 @@
  (% class="wikigeneratedid" id="HFigure142013MappingsfromSDMXdatatypestoVTLBasicScalarTypes-1" %)
  **Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types**
--In case a different default conversion is desired, it can be achieved through the CustomTypeScheme and CustomType [[artefacts>>doc:xwiki:Glossary.Artefact.WebHome]] (see also the section Transformations and Expressions of the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] information model).
++In case a different default conversion is desired, it can be achieved through the CustomTypeScheme and CustomType artefacts (see also the section Transformations and Expressions of the SDMX information model).
--The custom output formats can be specified by means of the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] formatting mask described in the section "Type Conversion and Formatting Mask" of the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Reference Manual. Such a section describes the masks for the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar types "number", "integer", "date", "time", "time_period" and "duration" and gives examples. As for the types "string" and "boolean" the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] conventions are extended with some other special characters as described in the following table.
++The custom output formats can be specified by means of the VTL formatting mask described in the section "Type Conversion and Formatting Mask" of the VTL Reference Manual. Such a section describes the masks for the VTL basic scalar types "number", "integer", "date", "time", "time_period" and "duration" and gives examples. As for the types "string" and "boolean" the VTL conventions are extended with some other special characters as described in the following table.
  (% style="width:713.294px" %)
  |(% colspan="2" style="width:710px" %)VTL special characters for the formatting masks
@@ -792,26 +792,26 @@
  |\|(% style="width:486px" %)prefix for the special characters that must appear in the mask
  |N|(% style="width:486px" %)fixed number of digits used in the preceding textual representation of the month or the day
--The default conversion, either standard or customized, can be used to deduce automatically the [[representation>>doc:xwiki:Glossary.Representation.WebHome]] of the [[components>>doc:xwiki:Glossary.Component.WebHome]] of the result of a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformation. In alternative, the [[representation>>doc:xwiki:Glossary.Representation.WebHome]] of the resulting [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[Dataflow>>doc:xwiki:Glossary.Dataflow.WebHome]] can be given explicitly by providing its DataStructureDefinition. In other words, the [[representation>>doc:xwiki:Glossary.Representation.WebHome]] specified in the [[DSD>>doc:xwiki:Glossary.Data structure definition.WebHome]], if available, overrides any default conversion{{footnote}}The representation given in the DSD should obviously be compatible with the VTL data type.{{/footnote}}.
++The default conversion, either standard or customized, can be used to deduce automatically the representation of the components of the result of a VTL Transformation. In alternative, the representation of the resulting SDMX Dataflow can be given explicitly by providing its DataStructureDefinition. In other words, the representation specified in the DSD, if available, overrides any default conversion{{footnote}}The representation given in the DSD should obviously be compatible with the VTL data type.{{/footnote}}.
  === 12.4.5 Null Values ===
--In the conversions from [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] to [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] it is assumed by default that a missing value in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] becomes a NULL in [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]]. After the conversion, the NULLs can be manipulated through the proper [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] operators.
++In the conversions from SDMX to VTL it is assumed by default that a missing value in SDMX becomes a NULL in VTL. After the conversion, the NULLs can be manipulated through the proper VTL operators.
--On the other side, the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] programs can produce in output NULL values for [[Measures>>doc:xwiki:Glossary.Measure.WebHome]] and [[Attributes>>doc:xwiki:Glossary.Attribute.WebHome]] (Null values are not allowed in the Identifiers). In the conversion from [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], it is assumed that a NULL in [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] becomes a missing value in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]]. In the conversion from [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]], the default assumption can be overridden, separately for each [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar type, by specifying which the value that represents the NULL in [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] is. This can be specified in the [[attribute>>doc:xwiki:Glossary.Attribute.WebHome]] "nullValue" of the CustomType [[artefact>>doc:xwiki:Glossary.Artefact.WebHome]] (see also the section Transformations and Expressions of the [[SDMX information model>>doc:xwiki:Glossary.SDMX Information Model.WebHome]]). A CustomType belongs to a CustomTypeScheme, which can be referenced by one or more TransformationScheme (i.e. [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] programs). The overriding assumption is applied for all the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] [[Dataflows>>doc:xwiki:Glossary.Dataflow.WebHome]] calculated in the TransformationScheme.
++On the other side, the VTL programs can produce in output NULL values for Measures and Attributes (Null values are not allowed in the Identifiers). In the conversion from VTL to SDMX, it is assumed that a NULL in VTL becomes a missing value in SDMX. In the conversion from VTL to SDMX, the default assumption can be overridden, separately for each VTL basic scalar type, by specifying which the value that represents the NULL in SDMX is. This can be specified in the attribute "nullValue" of the CustomType artefact (see also the section Transformations and Expressions of the SDMX information model). A CustomType belongs to a CustomTypeScheme, which can be referenced by one or more TransformationScheme (i.e. VTL programs). The overriding assumption is applied for all the SDMX Dataflows calculated in the TransformationScheme.
  === 12.4.6 Format of the literals used in VTL Transformations ===
--The [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] programs can contain literals, i.e. specific values of certain data types written directly in the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] definitions or expressions. The [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] does not prescribe a specific format for the literals and leave the specific [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] systems and the definers of [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Transformations free of using their preferred formats.
++The VTL programs can contain literals, i.e. specific values of certain data types written directly in the VTL definitions or expressions. The VTL does not prescribe a specific format for the literals and leave the specific VTL systems and the definers of VTL Transformations free of using their preferred formats.
--Given this discretion, it is essential to know which are the external [[representations>>doc:xwiki:Glossary.Representation.WebHome]] adopted for the literals in a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] program, in order to interpret them correctly. For example, if the external format for the dates is YYYY-MM-DD the date literal 2010-0102 has the meaning of 2^^nd^^ January 2010, instead if the external format for the dates is YYYY-DD-MM the same literal has the meaning of 1^^st^^ February 2010.
++Given this discretion, it is essential to know which are the external representations adopted for the literals in a VTL program, in order to interpret them correctly. For example, if the external format for the dates is YYYY-MM-DD the date literal 2010-0102 has the meaning of 2^^nd^^ January 2010, instead if the external format for the dates is YYYY-DD-MM the same literal has the meaning of 1^^st^^ February 2010.
--Hereinafter, i.e. in the [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] implementation of the [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]], it is assumed that the literals are expressed according to the "default output format" of the table of the previous paragraph ("Mapping [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar types to [[SDMX>>doc:xwiki:Glossary.Statistical data and metadata exchange.WebHome]] data types") unless otherwise specified.
++Hereinafter, i.e. in the SDMX implementation of the VTL, it is assumed that the literals are expressed according to the "default output format" of the table of the previous paragraph ("Mapping VTL basic scalar types to SDMX data types") unless otherwise specified.
--A different format can be specified in the [[attribute>>doc:xwiki:Glossary.Attribute.WebHome]] "vtlLiteralFormat" of the CustomType [[artefact>>doc:xwiki:Glossary.Artefact.WebHome]] (see also the section Transformations and Expressions of the [[SDMX information model>>doc:xwiki:Glossary.SDMX Information Model.WebHome]]).
++A different format can be specified in the attribute "vtlLiteralFormat" of the CustomType artefact (see also the section Transformations and Expressions of the SDMX information model).
--Like in the case of the conversion of NULLs described in the previous paragraph, the overriding assumption is applied, for a certain [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar type, if a value is found for the vtlLiteralFormat [[attribute>>doc:xwiki:Glossary.Attribute.WebHome]] of the CustomType of such [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] basic scalar type. The overriding assumption is applied for all the literals of a related [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] TransformationScheme.
++Like in the case of the conversion of NULLs described in the previous paragraph, the overriding assumption is applied, for a certain VTL basic scalar type, if a value is found for the vtlLiteralFormat attribute of the CustomType of such VTL basic scalar type. The overriding assumption is applied for all the literals of a related VTL TransformationScheme.
--In case a literal is operand of a [[VTL>>doc:xwiki:Glossary.Validation and transformation language.WebHome]] Cast operation, the format specified in the Cast overrides all the possible otherwise specified formats.
++In case a literal is operand of a VTL Cast operation, the format specified in the Cast overrides all the possible otherwise specified formats.
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