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Introduction to DFDL for Date Handling: Concepts and Layering Explained

This guide explores the DFDL (Data Format Description Language) support for handling date values through calculated representations. It discusses the logical and physical layers involved in date formatting, specifically how dates are stored and parsed. The document outlines properties like `inputValueCalc`, `outputValueCalc`, and `outputLengthCalc`, housing packed-decimal representations and hidden layers. Additionally, it provides examples showcasing how to calculate and unparse date fields (MM/DD/YYYY) while avoiding common pitfalls in data representation.

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Introduction to DFDL for Date Handling: Concepts and Layering Explained

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  1. Calculated Values • DFDL supports limited layering • Properties: • inputValueCalc • outputValueCalc • outputLengthCalc • Note: inputLengthCalc is just length=“{ … }” 1

  2. Calculated Values Example M M D D Y Y • Logically, the data is a date. <element name=“d” type=“date”/> • Physically, it is stored as 6 packed-decimal digits, unsigned • Like so: 2

  3. Physical Layer’s Shape M M D D Y Y <sequence> <element name="mm" type="int“ /> <element name="dd" type="int“ /> <element name="yy" type="int“ /> </sequence> 3

  4. Physical Layer Representation M M D D Y Y <sequence dfdl:representation="binary" dfdl:numberRepresentation="packedDecimal" dfdl:decimalSigned="false“ > <element name="mm" type="int" dfdl:numberPattern="##“ /> <element name="dd" type="int" dfdl:numberPattern="##“ /> <element name="yy" type="int" dfdl:numberPattern="##“ /> </sequence> 4

  5. Hide Physical Layer M M D D Y Y Physical layer (hidden) Logical layer <sequence> <annotation><appinfo ...> <dfdl:hidden> <element name="pdate"> <complexType> • <sequence dfdl:representation="binary" • dfdl:numberRepresentation="packedDecimal" • dfdl:decimalSigned="false“ > • <element name="mm" type="int" • dfdl:numberPattern="##“ /> • <element name="dd" type="int" • dfdl:numberPattern="##“ /> • <element name="yy" type="int" • dfdl:numberPattern="##“ /> • </sequence> </complexType> </element> </dfdl:hidden> </appinfo></annotation> <element name="d" type="date"> … </element> 5

  6. Parsing: Calculate Logical from Physical M M D D Y Y dfdl:property annotations to avoid quoting hell <sequence> … hidden pdate here … <element name="d" type="date"> <annotation><appinfo> <dfdl:format> <dfdl:property name="inputValueCalc"> { fn:date(fn:concat(if ( ../pdate/yy > 50 ) then "19" else "20", fn:string(../pdate/yy), "-", fn:string(../pdate/mm), "-", fn:string(../pdate/dd))) } </dfdl:property> </dfdl:format> </appinfo></annotation> </element> 6

  7. Unparsing: Calculate Physical from Logical M M D D Y Y <sequence dfdl:representation="binary" dfdl:numberRepresentation="packedDecimal" dfdl:decimalSigned="false" <element name="mm" type="int" dfdl:numberPattern="##" dfdl:outputValueCalc="{ fn:month-from-date(../d) }" /> <element name="dd" type="int" dfdl:numberPattern="##" dfdl:outputValueCalc="{ fn:day-from-date(../d) }" /> <element name="yy" type="int" dfdl:numberPattern="##" dfdl:outputValueCalc="{ fn:year-from-date(../d) idiv 100 }" /> </sequence> 7

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