View source for HL7 V3 Datatypes Implementation Notes

__TOC__

==Introduction==
This page provides some discussion about the HL7 V3 data types, and their XML representation. It is not constrained to a particular IHE profile, but it is hopefully useful to implementers of any CDA Release 2 based content profile, or any integration profile using HL7 V3 messages.

==Background==
The HL7 V3 data types are defined as an abstract specification, part of the HL7 V3 standard. The current version is Release 1, with Release 2 being in the final stages of development. This discussion is strictly about Release 1 of the HL7 V3 data types.

The abstract data types specification defines the properties of the data types. The XML Implementable Technology Specification (XML ITS) defines how the data types are represented in XML. HL7 publishes XML schemas for the V3 data types, which express '''most''' of the properties defined in the abstract specification, however certain rules are impossible to define using the XML schema language. This is one of the reasons that the schemas published by HL7 are informative artifacts, and are not sufficient to implement the full semantics of the V3 data types.

The schemas provided by HL7 are part of the V3 normative editions. The ones part of the 2008 Normative Edition are at ftp://ftp.ihe.net/TF_Implementation_Material/ITI/schema/HL7V3/NE2008/coreschemas/

==Implementation notes==
The HL7 V3 Data Types specification is one of the more stable and robust parts of the HL7 V3 standard. For anyone tasked with implementing and supporting HL7 V3 messaging, or CDA Release 2 document creation or processing, it will be quite useful to have a single common reusable implementation of the HL7 V3 data types.

The abstract implementation describes the relationships among the various data types, and the XML ITS tries to follow these relationships as close as possible. The HL7 V3 data types have rich semantics, and this results in a quite complicated schema, and also in a complex object-oriented implementation. Note that HL7 has an additional [http://www.hl7.org/v3ballot/html/infrastructure/itsuml/datatypes-its-uml.htm UML ITS for the HL7 V3 data types], which may be useful for certain development environments, and the HL7 RIM Based Application Architecture (RIMBAA) workgroup has a [http://www.hl7.org/Special/committees/java/index.cfm Java-based implementation for V3 data types] as part of its Java API for the V3 RIM.

While all major development platforms have tools to automatically generate code based on XML schema, many are not suited to properly handle the recursive definitions and generic type extensions used by the HL7 V3 data types. To illustrate this point the following sections will go through the definition of a particular data type to see how its properties are defined.
===Overview of V3 Data Type Definitions===
==== The Starting Point ====
The following question was asked on the 2009 NA Connectathon mailing list:
<pre>
according to the basic schema datatypes-base.xsd, an element of type EN may have sub-elements 
like given, family, prefix and so on.
 
now,
 - "given" is of type "en.given"
 - "en.given" restricts "ENXP"
 - "ENXP" extends "ST"
 - "ST" restricts "ED"
 - "ED" extends "BIN"
 - "BIN" extends "ANY"
 - "ANY" doesn't restrict or extend anything

question: which XMLSchema simple type has to be used for "given"?
</pre>

In order to answer the question, let's follow the steps of the definition of an element of type ''en.given''.

==== Defining an XML Element ====
The simplest element definition in an XML schema may look something like this:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org" targetNamespace="urn:example:org">
<xs:element name="el1"/>
</xs:schema>
</pre>

This simply defines an element with name ''el1'', which belongs to the ''urn:example:org'' namespace. No other restrictions or properties are defined for this element. A minimal XML document, consisting only of this element may look something like this:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  We can have just the element here -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample1.xsd"/>
</pre>

Since there were no restrictions placed on the element in the schema, it can have text content, and any number of attributes or child elements:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  We can have the element with content-->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample1.xsd">Some content</el1>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  We can have the element with arbitrary attributes-->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample1.xsd" attr1="1"/>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  We can have the element even with arbitrary child elements-->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample1.xsd"><el2/></el1>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  We can have the element with arbitrary attributes, child elements and mixed content-->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample1.xsd" attr1="1">
    <el2/>
    Some text
    <el3>some other text</el3>
    more text
    <el4/>
</el1>
</pre>

All of the above examples are valid with respect to the schema.
====Defining a Complex Data Type in the Schema====
If we take the definition of the ANY data type from the HL7 V3 schema, and remove the ''abstract'' attribute, we can see what will happen if we define our element to be of the ANY data type. The schema will be something like this:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org"
    targetNamespace="urn:example:org">
    <xs:element name="el1" type="ANY"/>
     <!-- This definition of the ANY data type is identical to the one in the HL7 datatypes-base.xsd schema,
     except that it is not defined as an abstract data type. This allows the associated examples to illustrate
     the effect of defining a complex data type for an element -->
    <xs:complexType name="ANY">
        <xs:annotation>
            <xs:documentation> Defines the basic properties of every data value. This is an abstract
                type, meaning that no value can be just a data value without belonging to any
                concrete type. Every concrete type is a specialization of this general abstract
                DataValue type. </xs:documentation>
        </xs:annotation>
        <xs:attribute name="nullFlavor" type="NullFlavor" use="optional">
            <xs:annotation>
                <xs:documentation> An exceptional value expressing missing information and possibly
                    the reason why the information is missing. </xs:documentation>
            </xs:annotation>
        </xs:attribute>
    </xs:complexType>
    <xs:simpleType name="cs">
        <xs:annotation>
            <xs:documentation> Coded data in its simplest form, consists of a code. The code system
                and code system version is fixed by the context in which the value occurs. is used
                for coded attributes that have a single HL7-defined value set. </xs:documentation>
        </xs:annotation>
        <xs:restriction base="xs:token">
            <xs:pattern value="[^\s]+"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="NullFlavor">
        <xs:annotation>
            <xs:documentation>vocSet: T10609 (C-0-T10609-cpt)</xs:documentation>
        </xs:annotation>
        <xs:union memberTypes="NoInformation"/>
    </xs:simpleType>
    <xs:simpleType name="NoInformation">
        <xs:annotation>
            <xs:documentation>specDomain: S10610 (C-0-T10609-S10610-cpt)</xs:documentation>
        </xs:annotation>
        <xs:union memberTypes="Other Unknown">
            <xs:simpleType>
                <xs:restriction base="cs">
                    <xs:enumeration value="NI"/>
                    <xs:enumeration value="MSK"/>
                    <xs:enumeration value="NA"/>
                    <xs:enumeration value="UNC"/>
                </xs:restriction>
            </xs:simpleType>
        </xs:union>
    </xs:simpleType>
    <xs:simpleType name="Other">
        <xs:annotation>
            <xs:documentation>specDomain: S10616 (C-0-T10609-S10610-S10616-cpt)</xs:documentation>
        </xs:annotation>
        <xs:restriction base="cs">
            <xs:enumeration value="OTH"/>
            <xs:enumeration value="NINF"/>
            <xs:enumeration value="PINF"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="Unknown">
        <xs:annotation>
            <xs:documentation>specDomain: S10612 (C-0-T10609-S10610-S10612-cpt)</xs:documentation>
        </xs:annotation>
        <xs:union memberTypes="AskedButUnknown">
            <xs:simpleType>
                <xs:restriction base="cs">
                    <xs:enumeration value="UNK"/>
                    <xs:enumeration value="QS"/>
                    <xs:enumeration value="NASK"/>
                    <xs:enumeration value="TRC"/>
                </xs:restriction>
            </xs:simpleType>
        </xs:union>
    </xs:simpleType>
    <xs:simpleType name="AskedButUnknown">
        <xs:annotation>
            <xs:documentation>specDomain: S10614
            (C-0-T10609-S10610-S10612-S10614-cpt)</xs:documentation>
        </xs:annotation>
        <xs:restriction base="cs">
            <xs:enumeration value="ASKU"/>
            <xs:enumeration value="NAV"/>
        </xs:restriction>
    </xs:simpleType>
</xs:schema>
</pre>

The bulk of the schema is taken by the vocabulary definitions of the allowable values for the single attribute, ''nullFlavor'', defined by the ''ANY'' data type. Besides this new optional attribute, nothing else is defined for this data type, but this actually implies certain things about it.

The first example shows the use of the optional ''nullFalvor'' attribute:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type ANY which means that the only valid addition to 
    the element is the nullFlavor attribute -->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample2.xsd" nullFlavor="OTH"/>
</pre>

There is nothing in the definition of the ''ANY'' data type describing the content of an element of this data type. This lack of description, however, implies that there is no content allowed (i.e. it defines an '''empty content model'''). The following examples are invalid for various reasons:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!-- el1 is now of type ANY, which has an empty content type, so no text 
    content is allowed. Therefore this example is invalid -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample2.xsd">Some content</el1>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type ANY, which has only one defined attribute, "nullFlavor", so no 
    other attributes are allowed. Therefore this example is invalid -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample2.xsd" attr1="1"/>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!-- el1 is now of type ANY, which has an empty content type, so no chldren are allowed. 
    Therefore this example is invalid -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample2.xsd"><el2/></el1>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type ANY, which has an empty content type, so no chldren, text content, 
    or attributes (other than nullFlavor) are allowed. 
    Therefore none of the additional XML attributes or children are valid -->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample2.xsd" attr1="1">
    <el2/>
    Some text
    <el3>some other text</el3>
    more text
    <el4/>
</el1>
</pre>

====Extending a Complex Data Type====
In order to take the next step along the type hierarchy, we can now restore the ''ANY'' data type to be an abstract data type, and use the ''BIN'' data type in the definition of our element. 

In the HL7 V3 schema, the ''BIN'' data type is also defined as an abstract data type, so the definition will be modified to make it a regular data type. Other than that, the definition is identical to the one in the HL7 V3 schema. The ''BIN'' data type defines two additions to the ''ANY'' datatype - the ''representation'' attribute, and allowing ''mixed content'' for elements of this data type. In general, ''mixed content'' means that an element can have child elements and/or text content. In this particulr case ''BIN'' has no child elements defined, so the ''mixed content'' definition simply allows text content to be present for elements of this data type.
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org"
    targetNamespace="urn:example:org">
    <xs:element name="el1" type="BIN"/>
     <!-- This definition of the BIN data type is identical to the one in the HL7 datatypes-base.xsd schema,
     except that it is not defined as an abstract data type. This allows the associated examples to illustrate
     the effect of defining an extension of a complex data type for an element -->
    <xs:complexType name="BIN" mixed="true">
        <xs:annotation>
            <xs:documentation>
                Binary data is a raw block of bits. Binary data is a
                protected type that MUST not be used outside the data
                type specification.
            </xs:documentation>
        </xs:annotation>
        <xs:complexContent>
            <xs:extension base="ANY">
                <xs:attribute name="representation" use="optional" type="BinaryDataEncoding" default="TXT">
                    <xs:annotation>
                        <xs:documentation>
                            Specifies the representation of the binary data that
                            is the content of the binary data value.
                        </xs:documentation>
                    </xs:annotation>
                </xs:attribute>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>
    <xs:simpleType name="BinaryDataEncoding">
        <xs:restriction base="xs:NMTOKEN">
            <xs:enumeration value="B64"/>
            <xs:enumeration value="TXT"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:complexType name="ANY" abstract="true">
        <xs:annotation>
            <xs:documentation> Defines the basic properties of every data value. This is an abstract
                type, meaning that no value can be just a data value without belonging to any
                concrete type. Every concrete type is a specialization of this general abstract
                DataValue type. </xs:documentation>
        </xs:annotation>
        <xs:attribute name="nullFlavor" type="NullFlavor" use="optional">
            <xs:annotation>
                <xs:documentation> An exceptional value expressing missing information and possibly
                    the reason why the information is missing. </xs:documentation>
            </xs:annotation>
        </xs:attribute>
    </xs:complexType>
    <xs:simpleType name="cs">
        <xs:annotation>
            <xs:documentation> Coded data in its simplest form, consists of a code. The code system
                and code system version is fixed by the context in which the value occurs. is used
                for coded attributes that have a single HL7-defined value set. </xs:documentation>
        </xs:annotation>
        <xs:restriction base="xs:token">
            <xs:pattern value="[^\s]+"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="NullFlavor">
        <xs:annotation>
            <xs:documentation>vocSet: T10609 (C-0-T10609-cpt)</xs:documentation>
        </xs:annotation>
        <xs:union memberTypes="NoInformation"/>
    </xs:simpleType>
    <xs:simpleType name="NoInformation">
        <xs:annotation>
            <xs:documentation>specDomain: S10610 (C-0-T10609-S10610-cpt)</xs:documentation>
        </xs:annotation>
        <xs:union memberTypes="Other Unknown">
            <xs:simpleType>
                <xs:restriction base="cs">
                    <xs:enumeration value="NI"/>
                    <xs:enumeration value="MSK"/>
                    <xs:enumeration value="NA"/>
                    <xs:enumeration value="UNC"/>
                </xs:restriction>
            </xs:simpleType>
        </xs:union>
    </xs:simpleType>
    <xs:simpleType name="Other">
        <xs:annotation>
            <xs:documentation>specDomain: S10616 (C-0-T10609-S10610-S10616-cpt)</xs:documentation>
        </xs:annotation>
        <xs:restriction base="cs">
            <xs:enumeration value="OTH"/>
            <xs:enumeration value="NINF"/>
            <xs:enumeration value="PINF"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="Unknown">
        <xs:annotation>
            <xs:documentation>specDomain: S10612 (C-0-T10609-S10610-S10612-cpt)</xs:documentation>
        </xs:annotation>
        <xs:union memberTypes="AskedButUnknown">
            <xs:simpleType>
                <xs:restriction base="cs">
                    <xs:enumeration value="UNK"/>
                    <xs:enumeration value="QS"/>
                    <xs:enumeration value="NASK"/>
                    <xs:enumeration value="TRC"/>
                </xs:restriction>
            </xs:simpleType>
        </xs:union>
    </xs:simpleType>
    <xs:simpleType name="AskedButUnknown">
        <xs:annotation>
            <xs:documentation>specDomain: S10614
            (C-0-T10609-S10610-S10612-S10614-cpt)</xs:documentation>
        </xs:annotation>
        <xs:restriction base="cs">
            <xs:enumeration value="ASKU"/>
            <xs:enumeration value="NAV"/>
        </xs:restriction>
    </xs:simpleType>
</xs:schema>
</pre>

The first example shows the new attribute added to the ''el1'' element. Note that while the example is valid according to the schema above, the presence of the ''representation'' attribute doesn't really make sense, since it refers to the text content of the element, and ''el1'' has no content. Since this is valid XML, however, it is important for implementers to realize that there are semantic properties which have to handled beyond XML schema validation. In this case, the ''representation'' attribute must be ignored, and the ''nullFlavor'' attribute must be processed as denoting that the element is indeed empty, and possibly the reason for it.
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type BIN which means that in addition to the nullFlavor attribute
there is another attribute, called representation-->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample3.xsd" nullFlavor="OTH" representation="TXT"/>
</pre>

The second example shows ''el1'' with text content. Note again, that, purely in XML Schema terms, one could add the ''nullFlavor'' attribute to the element, but this would make for an invalid HL7 data type, because the data types specification clearly defines the meaning of the ''nullFlavor'' attribute, and it must not be used if an element of a particular data type is not null.

Another thing to notice is that the ''representation'' attribute is not present. This is valid from both a purely XML Schema point of view, and from an HL7 point of view, because the attribute is optional, and it has a default value of <tt>TXT</tt>, which is, in fact, the representation shown in the example:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!-- el1 is now of type BIN, which was defined of mixed content, so text content is allowed. Therefore this example is valid -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample3.xsd">Some content</el1>
</pre>
An example showing Base 64 encoded data is presented as part of the ''ED'' data type discussion.

The rest of the examples show how adding extra attributes and/or child elements make the XML invalid with respect to the ''BIN'' data type as defined in the schema.
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type BIN, which has only two defined attributes, "nullFlavor" and "representation", 
    so no other attributes are allowed. Therefore this example is invalid -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample3.xsd" attr1="1"/>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type BIN, which has a mixed content type, but no child elements are defined.
    This practically restricts the BIN content type to only text content. Therefore this example is invalid -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample3.xsd"><el2/></el1>
</pre>

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type BIN, which has a mixed content type, but no child elements are defined.
    This practically restricts the BIN content type to only text content. so no child elements or 
    additional attributes (other than nullFlavor or representation) are allowed. 
    Therefore this example is invalid -->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample3.xsd" attr1="1" representation="TXT">
    <el2/>
    Some text
    <el3>some other text</el3>
    more text
    <el4/>
</el1>
</pre>

====Further Extensions====
The ''ED'' data type further extends ''BIN'' by adding pore properties to the abstract data type. Since ED is not abstract itself, the sample schema now can use the HL7 V3 data types directly, which is done by including the relevant schema. It is important to notice that the sample schema and all the examples use the ''urn:example:org'' namespace, and this can be done even when we include the HL7 V3 data types schema. This is possible because the data types XML schemas are defined without a target namespace. This is sometimes referred to as ''chameleon schema'' based on the property of such schemas that all of their definitions become part of the namespace of the including schema.

Defining ''el1'' to be of type ''ED'' would look something like this:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org"
    targetNamespace="urn:example:org">
    <xs:include schemaLocation="datatypes-base.xsd"/>
    <xs:element name="el1" type="ED"/>
</xs:schema>
</pre>

The following example shows the ''el1'' element with content appropriate for the ED data type. There are two child elements defined, ''reference'' and ''thumbnail'', and several new attributes are added. The HL7 V3 Data Types specification and the published HL7 V3 data types schema provide complete details of the meaning and definitions of these extensions. One notable detail is the data type of the ''thumbnail'' element - it is a restriction on ''ED'' itself, which is done to explicitly prohibit a thumbnail from having a thumbnail, while keeping the thumbnail's data representation the same as the data represented by ''ED''. Such recursion in the definition of the HL7 V3 data types is common, and this feature of XML Schema is supported by most toolkits. 

The example shows the data both as content in the ED element, and as a reference. In most cases either one or the other method would be used, although using both is valid with regards to the XML Schema, and to the HL7 V3 Data Types specification.

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type ED which means that in addition to the attributes from the BIN data type, 
    there are other attributes, and two child elements defined. The ED data type has mixed content, so the child
    elements can co-exist with the text content -->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample4.xsd" representation="B64"  mediaType="application/pdf"
    integrityCheck="ODMwZDZjOTE5NjFiNzNjZDM1OTkwMWY2M2QwZDlkMDM1MzNiZGU5MjU4NTYwNDQ0MDcwMmNhODZmZGFlNjM3Nw==" 
    integrityCheckAlgorithm="SHA-256">
    <reference value="http://wiki.ihe.net/images/d/de/Sample.pdf"/>
    JVBERi0xLjQKJcOkw7zDtsOfCjIgMCBvYmoKPDwvTGVuZ3RoIDMgMCBSL0ZpbHRlci9GbGF0ZURl
    Y29kZT4+CnN0cmVhbQp4nHVRu2rEMBDs/RVbB6Ts6n0gBPGdXaQ7MKQI6fLoArkmvx+NZDlFCIZl
    [...snip...]
    Q0IzNzI3NDkzOUJFQzlGPiBdCi9Eb2NDaGVja3N1bSAvQ0JFMkI5RkFFM0I2RDE1RDI4MUQxMzZD
    NjU0MTM2MEQKPj4Kc3RhcnR4cmVmCjQ0MDM1CiUlRU9GCg== 
    <thumbnail representation="B64" mediaType="image/png">
        iVBORw0KGgoAAAANSUhEUgAAAEwAAABhCAIAAADzx9CUAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
        jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAAuJJREFU
        [...snip...]
        UuWxSSry6F42iSZKlccmqcije9kkmihVHpukIo/u/V9NarvNd35/lqS5P/dUW6ft/AFlHiFy1UdU
        qQAAAABJRU5ErkJggg== 
    </thumbnail>
</el1>
</pre>

The next example shows a much simple use of the ED data type. Since in this case the data is simple text, both the ''representation'' and ''mediaType'' attributes can be omitted, since their default values (<tt>TXT</tt> and <tt>text/plain</tt> respectively) represent plain text.
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!-- el1 is now of type ED, which is defined of mixed content, so text content is allowed. Therefore this example is valid -->
<el1 xmlns="urn:example:org"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample4.xsd">Some content</el1>
</pre>
In fact, this use of the ''ED'' data type is so common, that a separate type to represent plain text was created - the ''ST'' data type.

====Restricting a Complex Data Type====
The ''ST'' data type is defined by restricting ''ED'' to represent just simple text data. Only text content is allowed, and only the attributes which are appropriate for text content are retained. The sample schema, defining ''el1'' to be of type ''ST'' looks like this:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org"
    targetNamespace="urn:example:org">
    <xs:include schemaLocation="datatypes-base.xsd"/>
    <xs:element name="el1" type="ST"/>
</xs:schema>
</pre>

The example shows ''el1'' with text content, and the ''language'' attribute.
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type ST which restricts most of the options available in the ED data type. Only text content 
    is allowed, and besides nullFlavor, only 3 attributes are allowed, two of which, representation and mediaType are fixed
    representing plain text. The only other attribute allowed is language.
 -->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample5.xsd" language="en-US">
    Sample text
</el1>
</pre>

====Name Parts and Names====
The ''ENXP'' data type represents a particular kind of text data, which corresponds to a part of an entity's name. Most often these are person names. Each name part may have a type, signifying the role of the particular name part in the name, and a qualifier, which provides further information about the type. These new attributes are defined by extending the ''ST'' data type. The following sample schema defines ''el1'' to be of type ''ENXP'':
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org"
    targetNamespace="urn:example:org">
    <xs:include schemaLocation="datatypes-base.xsd"/>
    <xs:element name="el1" type="ENXP"/>
</xs:schema>
</pre>

A generic name part can represent a person's given name by specifying the corresponding name part type, as in this example:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type ENXP which is used to represent Entity Name Parts. It is an extention of ST. Only text content 
    is allowed, and two new attributes are added - partType and qualifiers, which are used to define the name part.
 -->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample6.xsd" partType="GIV">John</el1>
</pre>

In order to provide more readable XML instances, the HL7 V3 Datatypes schema constrains the generic ''ENXP'' data type to specific data types for given name, family name, etc. For example, if we want to define ''el1'' to be a given name, we can assign it the ''en.given'' data type:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org"
    targetNamespace="urn:example:org">
    <xs:include schemaLocation="datatypes-base.xsd"/>
    <xs:element name="el1" type="en.given"/>
</xs:schema>
</pre>

The ''en.given'' data type constrains ''ENXP'' by making the ''type'' attribute fixed, with a value of <tt>GIV</tt>. The ''qualifier'' attribute can be still used to further define the given name. The example of a given name (with a qualifier that this is the person's preferred name to be called by) now looks like this:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type en.given which is used to represent given names. It is a restriction of ENXP. Only text content 
    is allowed, and partType is fixed to "GIV", while qualifiers are still allowed to further define the given name.
 -->
<el1 xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample7.xsd" qualifier="CL">John</el1>
</pre>

Of course, this is still not very readable, but when a person's name is defined, it is usually the whole name which gets a ''PN'' data type, and the parts are defined within that data type with readable names. The following sample schema and example demonstrate that:

<pre>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:example:org"
    targetNamespace="urn:example:org">
    <xs:include schemaLocation="datatypes-base.xsd"/>
    <xs:element name="name" type="PN"/>
</xs:schema>
</pre> 

This allows for much more readable XML instance:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<!--  el1 is now of type PN which contains pre-defined name parts of specific data types -->
<name xmlns="urn:example:org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:example:org sample8.xsd">
    <given qualifier="CL">John</given>
    <family>Doe</family>
</name>
</pre> 
=== Impact on Implementations ===
Code generating tools provide a great starting point for implementations. Implementers, however, need to have basic understanding of the HL7 V3 Abstract Data Types definition, of the XML ITS for V3 Data Types, and of the XML Schema Language in general. This will allow them to "fill in the gaps" where the automated tools cannot determine how a particular type can be implemented, and further more, apply the proper constraints where the XML schema is unable to do so.

Given the above example, an implementer can create the necessary structures for names and name parts. Once an HL7 V3 data types implementation is available, any HL7 V3 RIM-based structure can reuse that implementation. Code generation tools can build the necessary pieces corresponding to the RIM classes, and anything that is built for the data types can be simply substituted with the common implementation.

=== Files ===
The examples presented here, and few more files [http://ihewiki.wustl.edu/wiki/images/2/25/HL7_V3_Datatypes_discussion.zip are available online] from the Washington University - St. Louis IHE Wiki. The ZIP archive includes the HL7 V3 data types schema files published as part of the HL7 V3 2008 Normative Edition. The following copyright notice applies to them:
<pre>
Copyright (c) 2001 - 2008 Health Level Seven. All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:
  1. Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
     documentation and/or other materials provided with the distribution.
  3. All advertising materials mentioning features or use of this software
     must display the following acknowledgment:
       This product includes software developed by Health Level Seven.
 
  THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  SUCH DAMAGE.
</pre>
[[Category:Profile Implementations]]