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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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... ... @@ -19,7 +19,6 @@
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 -
23 23  === 12.2.1 Introduction ===
24 24  
25 25  The VTL can manipulate SDMX artefacts (or objects) by referencing them through predefined conventional names (aliases).
... ... @@ -49,8 +49,10 @@
49 49  
50 50  The generic structure of the URN is the following:
51 51  
52 -SDMXprefix.SDMX-IM-package-name.class-name=agency-id:maintainedobject-id (maintainedobject-version).*container-object-id.object-id
51 +SDMXprefix.SDMX-IM-package-name.class-name=agency-id:maintainedobject-id
53 53  
53 +(maintainedobject-version).*container-object-id.object-id
54 +
54 54  The **SDMXprefix** is "urn:sdmx:org", always the same for all SDMX artefacts.
55 55  
56 56  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".
... ... @@ -71,19 +71,24 @@
71 71  
72 72  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).
73 73  
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.
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
75 75  
76 76  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:
77 77  
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)
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 +
79 79  * if the artefact is a Concept (the object-id is the name of the Concept)
80 80  
81 81  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}}:
82 82  
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)'
87 +'urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=AG:DFR(1.0.0)' <-
86 86  
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 +
87 87  === 12.2.3 Abbreviation of the URN ===
88 88  
89 89  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.
... ... @@ -174,7 +174,6 @@
174 174  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.
175 175  
176 176  == 12.3 Mapping between SDMX and VTL artefacts ==
177 -
178 178  === 12.3.1. When the mapping occurs ===
179 179  
180 180  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.
... ... @@ -534,7 +534,6 @@
534 534  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.
535 535  
536 536  == 12.4 Mapping between SDMX and VTL Data Types ==
537 -
538 538  === 12.4.1 VTL Data types ===
539 539  
540 540  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.
... ... @@ -726,20 +726,27 @@
726 726  |IdentifiableReference|Metadata type – not applicable
727 727  |DataSetReference|Metadata type – not applicable
728 728  
729 -**Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types**
733 +додол
730 730  
735 +==== Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types ====
736 +
731 731  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).
732 732  
733 -=== 12.4.4 Mapping VTL basic scalar types to SDMX data types ===
739 +1.
740 +11.
741 +111. Mapping VTL basic scalar types to SDMX data types
734 734  
735 735  The following table describes the default conversion from the VTL basic scalar types to the SDMX data types .
736 736  
737 737  |(((
738 738  VTL basic
747 +
739 739  scalar type
740 740  )))|(((
741 741  Default SDMX data type
751 +
742 742  (BasicComponentDataType
753 +
743 743  )
744 744  )))|Default output format
745 745  |String|String|Like XML (xs:string)
... ... @@ -749,15 +749,17 @@
749 749  |Time|StandardTimePeriod|<date>/<date> (as defined above)
750 750  |time_period|(((
751 751  ReportingTimePeriod
763 +
752 752  (StandardReportingPeriod)
753 753  )))|(((
754 754   YYYY-Pppp
767 +
755 755  (according to SDMX )
756 756  )))
757 757  |Duration|Duration|Like XML (xs:duration) PnYnMnDTnHnMnS
758 758  |Boolean|Boolean|Like XML (xs:boolean) with the values "true" or "false"
759 759  
760 -**Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types**
773 +==== Figure 14 – Mappings from SDMX data types to VTL Basic Scalar Types ====
761 761  
762 762  In case a different default conversion is desired, it can be achieved through the CustomTypeScheme and CustomType artefacts (see also the section
763 763  
... ... @@ -815,13 +815,17 @@
815 815  
816 816  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}}.
817 817  
818 -=== 12.4.3 Null Values ===
831 +1.
832 +11.
833 +111. Null Values
819 819  
820 820  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.
821 821  
822 822  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.
823 823  
824 -=== 12.4.5 Format of the literals used in VTL Transformations ===
839 +1.
840 +11.
841 +111. Format of the literals used in VTL Transformations
825 825  
826 826  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.
827 827  
... ... @@ -835,6 +835,7 @@
835 835  
836 836  In case a literal is operand of a VTL Cast operation, the format specified in the Cast overrides all the possible otherwise specified formats.
837 837  
855 +
838 838  ----
839 839  
840 840  {{putFootnotes/}}