Hi Folks,
Please let me know of anything that is unclear. /Roger
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3. Fixed length, nillable, composite, no choice
A composite field is one that is composed of parts. There is no separator
between the parts. The parts may be fixed length or variable length. The parts
are non-nillable, although the composite field itself may be nillable.
This section deals with composite fields containing parts that are all fixed
length and the field is nillable.
We will create a DFDL schema for a "DateTime" field that has a date and time,
separated by T. Here is a sample value:
20220919T134700Z
That is one value with 8 parts:
The first four digits (2022) is the year.
The next two digits (09) is the month.
The next two digits (19) is the day.
The T separates the date from the time.
The 13 is the hour.
The 47 is the minute.
The 00 is the second.
The Z is the time zone.
In other words, the DateTime is September 19, 2022 at 1:47pm Zulu.
Here is another example of a valid DateTime value:
-
That value means no data was available to populate the field.
Field Requirements:
>> Fixed length (16)
>> Nillable, hyphen is the nil value
>> Composite, 8 parts
Here is an XML Schema declaration of DateTime, sans any DFDL properties (I
highlighted in yellow the field name - DateTime - and its part names):
<xs:element name="DateTime" nillable="true">
<xs:complexType>
<xs:sequence>
<xs:element name="Year">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{4}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Month">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="01"/>
<xs:enumeration value="02"/>
<xs:enumeration value="03"/>
<xs:enumeration value="04"/>
<xs:enumeration value="05"/>
<xs:enumeration value="06"/>
<xs:enumeration value="07"/>
<xs:enumeration value="08"/>
<xs:enumeration value="09"/>
<xs:enumeration value="10"/>
<xs:enumeration value="11"/>
<xs:enumeration value="12"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Day">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="DateTimeSeparator">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="T" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Hour">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Minute">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Second">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="TimeZone">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Z" />
</xs:restriction>
</xs:simpleType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
All parts have fixed length. To each part add these two DFDL properties:
dfdl:lengthKind="explicit"
dfdl:length="__"
For example, Year has a fixed length of 4. Here is its declaration, with the
DFDL properties (in yellow) added:
<xs:element name="Year"
dfdl:lengthKind="explicit"
dfdl:length="2">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{4}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
Use the same strategy for the other fields.
As I stated earlier, DateTime is nillable with hyphen as the nil value.
Further, DateTime has a complexType. That is a problem. See section 2 for a
complete discussion of the problem with nillable complexTypes and how to deal
with it.
Here's the DFDL schema for DateTime (the DFDL properties are shown in yellow):
<xs:element name="DateTime" nillable="true">
<xs:complexType>
<xs:sequence>
<xs:element name="Year"
dfdl:lengthKind="explicit"
dfdl:length="4">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{4}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Month"
dfdl:lengthKind="explicit"
dfdl:length="2">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="01"/>
<xs:enumeration value="02"/>
<xs:enumeration value="03"/>
<xs:enumeration value="04"/>
<xs:enumeration value="05"/>
<xs:enumeration value="06"/>
<xs:enumeration value="07"/>
<xs:enumeration value="08"/>
<xs:enumeration value="09"/>
<xs:enumeration value="10"/>
<xs:enumeration value="11"/>
<xs:enumeration value="12"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Day"
dfdl:lengthKind="explicit"
dfdl:length="2">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="DateTimeSeparator"
dfdl:lengthKind="explicit"
dfdl:length="1">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="T" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Hour"
dfdl:lengthKind="explicit"
dfdl:length="2">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Minute"
dfdl:lengthKind="explicit"
dfdl:length="2">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Second"
dfdl:lengthKind="explicit"
dfdl:length="2">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{2}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="TimeZone"
dfdl:lengthKind="explicit"
dfdl:length="1">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Z" />
</xs:restriction>
</xs:simpleType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
Notice that the last part (TimeZone) has no DFDL added. This is because I am
assuming that it is followed by the delimiter for the DateTime field.
Recall from section 2 that the workaround for nillable complexTypes is to
create a wrapper element that has a choice with two branches: the first branch
is a simple string element to deal with nil values and the second branch is (in
this case) the non-nil DateTime element. So the DFDL schema for our example has
this structure:
<xs:element name="DateTimeWrapper">
<xs:complexType>
<xs:choice dfdl:choiceLengthKind="implicit">
<xs:element name="DateTime_" type="xs:string" nillable="true"
dfdl:nilKind="literalValue"
dfdl:nilValue="-">
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:assert>{ fn:nilled(.) }</dfdl:assert>
</xs:appinfo>
</xs:annotation>
</xs:element>
<xs:element name="DateTime">
<!-- see above -->
</xs:element>
</xs:choice>
</xs:complexType>
</xs:element>
One last (important) point: When parsing input with Daffodil use the -V limited
option. The option instructs Daffodil to validate each part of the composite
field against the XSD facets. With this erroneous input value:
xxxx0919T134700Z
Daffodil gives this very helpful error message on parsing:
[error] Validation Error: Year failed facet checks due to: facet pattern(s):
[0-9]{4}
If you don't use the -V limited option, then Daffodil won't validate the parts
against the XSD facets. Consequently, Daffodil will not report any errors with
the above erroneous input. Why? Because if we ignore the facets in this element
declaration:
<xs:element name="Year"
dfdl:lengthKind="explicit"
dfdl:length="4">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{4}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
then it is simply saying that the input must be a string of length 4 and "xxxx"
certainly fits that specification.
