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Last modified by Artur on 2025/09/10 11:19
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edited by Helena
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edited by Helena
on 2025/06/16 13:20
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... ... @@ -19,6 +19,7 @@
19 19  This section does not explain the VTL language or any of the content published in the VTL guides. Rather, this is a description of how the VTL can be used in the SDMX context and applied to SDMX artefacts.
20 20  
21 21  == 12.2 References to SDMX artefacts from VTL statements ==
22 +
22 22  === 12.2.1 Introduction ===
23 23  
24 24  The VTL can manipulate SDMX artefacts (or objects) by referencing them through predefined conventional names (aliases).
... ... @@ -48,10 +48,8 @@
48 48  
49 49  The generic structure of the URN is the following:
50 50  
51 -SDMXprefix.SDMX-IM-package-name.class-name=agency-id:maintainedobject-id
52 +SDMXprefix.SDMX-IM-package-name.class-name=agency-id:maintainedobject-id (maintainedobject-version).*container-object-id.object-id
52 52  
53 -(maintainedobject-version).*container-object-id.object-id
54 -
55 55  The **SDMXprefix** is "urn:sdmx:org", always the same for all SDMX artefacts.
56 56  
57 57  The SDMX-IM-package-name** **is the concatenation of the string** **"sdmx.infomodel." with the package-name, which the artefact belongs to. For example, for referencing a Dataflow the SDMX-IM-package-name is "sdmx.infomodel.datastructure", because the class Dataflow belongs to the package "datastructure".
... ... @@ -72,24 +72,19 @@
72 72  
73 73  The maintainedobject-version is the version, according to the SDMX versioning rules, of the maintained object which the artefact belongs to (for example, possible versions might be 1.0, 2.3, 1.0.0, 2.1.0 or 3.1.2).
74 74  
75 -The container-object-id does not apply to the classes that can be referenced in VTL Transformations, therefore is not present in their URN
74 +The container-object-id does not apply to the classes that can be referenced in VTL Transformations, therefore is not present in their URN.
76 76  
77 77  The object-id is the name of the non-maintainable artefact (when the artefact is maintainable its name is already specified as the maintainedobject-id, see above), in particular it has to be specified:
78 78  
79 -* if the artefact is a Dimension, TimeDimension, Measure or
80 -
81 -DataAttribute (the object-id is the name of one of the artefacts above, which are data structure components)
82 -
78 +* if the artefact is a Dimension, TimeDimension, Measure or DataAttribute (the object-id is the name of one of the artefacts above, which are data structure components)
83 83  * if the artefact is a Concept (the object-id is the name of the Concept)
84 84  
85 85  For example, by using the URN, the VTL Transformation that sums two SDMX Dataflows DF1 and DF2 and assigns the result to a third persistent Dataflow DFR, assuming that DF1, DF2 and DFR are the maintainedobject-id of the three Dataflows, that their version is 1.0.0 and their Agency is AG, would be written as{{footnote}}Since these references to SDMX objects include non-permitted characters as per the VTL ID notation, they need to be included between single quotes, according to the VTL rules for irregular names.{{/footnote}}:
86 86  
87 -'urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=AG:DFR(1.0.0)' <-
83 +>(% style="font-size:16px" %) 'urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=AG:DFR(1.0.0)' <-
84 +>(% style="font-size:16px" %) 'urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=AG:DF1(1.0.0)' +
85 +>(% style="font-size:16px" %) 'urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=AG:DF2(1.0.0)'
88 88  
89 -'urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=AG:DF1(1.0.0)' +
90 -
91 -'urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=AG:DF2(1.0.0)'
92 -
93 93  === 12.2.3 Abbreviation of the URN ===
94 94  
95 95  The complete formulation of the URN described above is exhaustive but verbose, even for very simple statements. In order to reduce the verbosity through a simplified identifier and make the work of transformation definers easier, proper abbreviations of the URN are possible. Using this approach, the referenced artefacts remain intelligible in the VTL code by a human reader.
... ... @@ -98,10 +98,13 @@
98 98  
99 99  * The SDMXprefix can be omitted for all the SDMX objects, because it is a prefixed string (urn:sdmx:org), always the same for SDMX objects.
100 100  * The SDMX-IM-package-name** **can be omitted as well because it can be deduced from the class-name that follows it (the table of the SDMX-IM packages and classes that allows this deduction is in the SDMX 2.1 Standards - Section 5 - Registry Specifications, paragraph 6.2.3). In particular, considering the object classes of the artefacts that VTL can reference, the package is:
101 -** "datastructure" for the classes Dataflow, Dimension, TimeDimension, Measure, DataAttribute, o "conceptscheme" for the class Concept, o "codelist" for the class Codelist.
95 +** "datastructure" for the classes Dataflow, Dimension, TimeDimension, Measure, DataAttribute,
96 +** "conceptscheme" for the class Concept,
97 +** "codelist" for the class Codelist.
102 102  * The class-name can be omitted as it can be deduced from the VTL invocation. In particular, starting from the VTL class of the invoked artefact (e.g. dataset, component, identifier, measure, attribute, variable, valuedomain), which is known given the syntax of the invoking VTL operator{{footnote}}For the syntax of the VTL operators see the VTL Reference Manual{{/footnote}}, the SDMX class can be deduced from the mapping rules between VTL and SDMX (see the section "Mapping between VTL and SDMX" hereinafter){{footnote}}In case the invoked artefact is a VTL component, which can be invoked only within the invocation of a VTL data set (SDMX Dataflow), the specific SDMX class-name (e.g. Dimension, TimeDimension, Measure or DataAttribute) can be deduced from the data structure of the SDMX Dataflow, which the component belongs to.{{/footnote}}.
103 103  * If the agency-id is not specified, it is assumed by default equal to the agency-id of the TransformationScheme, UserDefinedOperatorScheme or RulesetScheme from which the artefact is invoked. For example, the agencyid can be omitted if it is the same as the invoking TransformationScheme and cannot be omitted if the artefact comes from another agency{{footnote}}If the Agency is composite (for example AgencyA.Dept1.Unit2), the agency is considered different even if only part of the composite name is different (for example AgencyA.Dept1.Unit3 is a different Agency than the previous one). Moreover the agency-id cannot be omitted in part (i.e., if a TransformationScheme owned by AgencyA.Dept1.Unit2 references an artefact coming from AgencyA.Dept1.Unit3, the specification of the agency-id becomes mandatory and must be complete, without omitting the possibly equal parts like AgencyA.Dept1){{/footnote}}. Take also into account that, according to the VTL consistency rules, the agency of the result of a Transformation must be the same as its TransformationScheme, therefore the agency-id can be omitted for all the results (left part of Transformation statements).
104 -* As for the maintainedobject-id, this is essential in some cases while in other cases it can be omitted: o if the referenced artefact is a Dataflow, which is a maintainable class, the maintainedobject-id is the dataflow-id and obviously cannot be omitted;
100 +* As for the maintainedobject-id, this is essential in some cases while in other cases it can be omitted:
101 +** if the referenced artefact is a Dataflow, which is a maintainable class, the maintainedobject-id is the dataflow-id and obviously cannot be omitted;
105 105  ** if the referenced artefact is a Dimension, TimeDimension, Measure, DataAttribute, which are not maintainable and belong to the DataStructure maintainable class, the maintainedobject-id is the dataStructure-id and can be omitted, given that these components are always invoked within the invocation of a Dataflow, whose dataStructure-id can be deduced from the SDMX structural definitions;
106 106  ** if the referenced artefact is a Concept, which is not maintainable and belong to the ConceptScheme maintainable class, the maintained object is the conceptScheme-id and cannot be omitted;
107 107  ** if the referenced artefact is a Codelist, which is a maintainable class, the maintainedobject-id is the codelist-id and obviously cannot be omitted.
... ... @@ -180,6 +180,7 @@
180 180  In the body of the Rulesets, the Codes and in general all the Values can be written without any other specification, because the artefact, which the Values are referred (Codelist, Concept) to can be deduced from the Ruleset signature.
181 181  
182 182  == 12.3 Mapping between SDMX and VTL artefacts ==
180 +
183 183  === 12.3.1. When the mapping occurs ===
184 184  
185 185  The mapping methods between the VTL and SDMX object classes allow transforming a SDMX definition in a VTL one and vice-versa for the artefacts to be manipulated. It should be remembered that VTL programs (i.e. Transformation Schemes) are represented in SDMX through the TransformationScheme maintainable class which is composed of Transformations (nameable artefacts). Each Transformation assigns the outcome of the evaluation of a VTL expression to a result: the input operands of the expression and the result can be SDMX artefacts. Every time a SDMX object is referenced in a VTL Transformation as an input operand, there is the need to generate a VTL definition of the object, so that the VTL operations can take place. This can be made starting from the SDMX definition and applying a SDMX-VTL mapping method in the direction from SDMX to VTL. The possible mapping methods from SDMX to VTL are described in the following paragraphs and are conceived to allow the automatic deduction of the VTL definition of the object from the knowledge of the SDMX definition.
... ... @@ -539,6 +539,7 @@
539 539  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.
540 540  
541 541  == 12.4 Mapping between SDMX and VTL Data Types ==
540 +
542 542  === 12.4.1 VTL Data types ===
543 543  
544 544  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.
... ... @@ -730,27 +730,20 @@
730 730  |IdentifiableReference|Metadata type – not applicable
731 731  |DataSetReference|Metadata type – not applicable
732 732  
733 -додол
732 +**Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types**
734 734  
735 -==== Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types ====
736 -
737 737  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).
738 738  
739 -1.
740 -11.
741 -111. Mapping VTL basic scalar types to SDMX data types
736 +=== 12.4.4 Mapping VTL basic scalar types to SDMX data types ===
742 742  
743 743  The following table describes the default conversion from the VTL basic scalar types to the SDMX data types .
744 744  
745 745  |(((
746 746  VTL basic
747 -
748 748  scalar type
749 749  )))|(((
750 750  Default SDMX data type
751 -
752 752  (BasicComponentDataType
753 -
754 754  )
755 755  )))|Default output format
756 756  |String|String|Like XML (xs:string)
... ... @@ -760,17 +760,15 @@
760 760  |Time|StandardTimePeriod|<date>/<date> (as defined above)
761 761  |time_period|(((
762 762  ReportingTimePeriod
763 -
764 764  (StandardReportingPeriod)
765 765  )))|(((
766 766   YYYY-Pppp
767 -
768 768  (according to SDMX )
769 769  )))
770 770  |Duration|Duration|Like XML (xs:duration) PnYnMnDTnHnMnS
771 771  |Boolean|Boolean|Like XML (xs:boolean) with the values "true" or "false"
772 772  
773 -==== Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types ====
763 +**Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types**
774 774  
775 775  In case a different default conversion is desired, it can be achieved through the CustomTypeScheme and CustomType artefacts (see also the section
776 776  
... ... @@ -828,17 +828,13 @@
828 828  
829 829  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}}.
830 830  
831 -1.
832 -11.
833 -111. Null Values
821 +=== 12.4.3 Null Values ===
834 834  
835 835  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.
836 836  
837 837  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.
838 838  
839 -1.
840 -11.
841 -111. Format of the literals used in VTL Transformations
827 +=== 12.4.5 Format of the literals used in VTL Transformations ===
842 842  
843 843  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.
844 844  
... ... @@ -852,7 +852,6 @@
852 852  
853 853  In case a literal is operand of a VTL Cast operation, the format specified in the Cast overrides all the possible otherwise specified formats.
854 854  
855 -
856 856  ----
857 857  
858 858  {{putFootnotes/}}