RE: [XSD question] Does ref'ing to the same global elementdeclaration mu

[Roger L Costello <costello@mitre.org>]

Hi Folks,

Thank you for your responses. Very good, ref'ing multiple times to a global element declaration does not violate DRY.

Below I have slightly modified the XML Schema. I created an xs:group and placed the ref's to Title and Publisher inside the xs:group. Now the Book and Magazine elements ref to the xs:group. In the previous XML Schema design there were two ref's to Title and two ref's to Publisher:

<xs:element ref="Title" />
<xs:element ref="Title" />
<xs:element ref="Publisher" />
<xs:element ref="Publisher" />

In the new design there is only one ref to Title and one ref to Publisher (the ref's are inside xs:group). But now there are two ref's to the xs:group

<xs:group ref="Title-and-Publisher" />
<xs:group ref="Title-and-Publisher" />

In the previous design there were four ref's:

<xs:element ref="Title" />
<xs:element ref="Title" />
<xs:element ref="Publisher" />
<xs:element ref="Publisher" />

In the new design there are also four ref's:

<xs:group ref="Title-and-Publisher" />
<xs:group ref="Title-and-Publisher" />
<xs:element ref="Title" />
<xs:element ref="Publisher" />

Suppose Book and Magazine have three common elements: Title, Publisher, and Author. In the old design there would be six ref's:

<xs:element ref="Title" />
<xs:element ref="Title" />
<xs:element ref="Publisher" />
<xs:element ref="Publisher" />
<xs:element ref="Author" />
<xs:element ref="Author" />

In the new design there would be five ref's:

<xs:group ref="Title-and-Publisher-and-Author" />
<xs:group ref="Title-and-Publisher-and-Author" />
<xs:element ref="Title" />
<xs:element ref="Publisher" />
<xs:element ref="Author" />

You have stated that ref's do not violate DRY. Here we see an opportunity to reduce the number of ref's by using xs:group. Is a design that uses less ref's more DRY-compliant than a design that uses more ref's?  /Roger 
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<xs:element name="Bookstore">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="Book" maxOccurs="unbounded">
                <xs:complexType>
                    <xs:sequence>
                        <xs:group ref="Title-and-Publisher" />
                        ...
                    </xs:sequence>
                </xs:complexType>
            </xs:element>
            <xs:element name="Magazine" maxOccurs="unbounded">
                <xs:complexType>
                    <xs:sequence>
                        <xs:group ref="Title-and-Publisher" />
                        ...
                    </xs:sequence>
                </xs:complexType>
            </xs:element>
        </xs:sequence>
    </xs:complexType>
</xs:element>

<xs:group name="Title-and-Publisher">
    <xs:sequence>
        <xs:element ref="Title" />
        <xs:element ref="Publisher" />
    </xs:sequence>
</xs:group>

<xs:element name="Title" type="xs:string" />
<xs:element name="Publisher" type="xs:string" />
...