Creating Sequences

By default, complex types in declare sequences of elements must appear in a conforming document. It turns out that you can also create sequences yourself using the <xsd:sequence> element.

For example, say that I want to let the borrower borrow not just books, but also a magazine. To do that, I can create a new group named booksAndMagazine. A group collects elements together. You can name groups, and you can then include a group in other elements using the <xsd:group> element and referring to the group by name:

<xsd:complexType name="transactionType">
    <xsd:element name="Lender" type="address"/>
    <xsd:element name="Borrower" type="address"/>
    <xsd:element ref="note" minOccurs="0"/>
    <xsd:choice>
        <xsd:element name="books" type="books"/>
        <xsd:element ref="book"/>
        <xsd:group ref="booksAndMagazine"/>
    <xsd:choice>
    <xsd:attribute name="borrowDate" type="xsd:date"/>
</xsd:complexType>

To create the group named booksAndMagazine, I use the <xsd:group> element; to ensure that the elements inside that group appear in a specific sequence, I use the <xsd:sequence> element this way:

<xsd:complexType name="transactionType">
    <xsd:element name="Lender" type="address"/>
    <xsd:element name="Borrower" type="address"/>
    <xsd:element ref="note" minOccurs="0"/>
    <xsd:choice>
        <xsd:element name="books" type="books"/>
        <xsd:element ref="book"/>
        <xsd:group ref="booksAndMagazine"/>
    <xsd:choice>
    <xsd:attribute name="borrowDate" type="xsd:date"/>
</xsd:complexType>

<xsd:complexType name="books">
    <xsd:element ref="book" minOccurs="0" maxOccurs="10" />
</xsd:complexType>

<xsd:group name="booksAndMagazine">
    <xsd:sequence>
        <xsd:element ref="books"/>
        <xsd:element ref="magazine"/>
    </xsd:sequence>
</xsd:group>

<xsd:element name="book">
    <xsd:complexType>
        <xsd:element name="bookTitle" type="xsd:string"/>
        <xsd:element name="pubDate" type="xsd:date" minOccurs='0'/>
        <xsd:element name="replacementValue" type="xsd:decimal"/>
        <xsd:element name="maxDaysOut">
           <xsd:simpleType base="xsd:integer">
                <xsd:maxExclusive value="14"/>
             </xsd:simpleType>
        </xsd:element>
        <xsd:attribute name="bookID" type="catalogID"/>
    </xsd:complexType>
</xsd:element>

<xsd:element name="magazine">
    <xsd:complexType>
        <xsd:element name="magazineTitle" type="xsd:string"/>
        <xsd:element name="pubDate" type="xsd:date" minOccurs='0'/>
        <xsd:element name="maxDaysOut">
            <xsd:simpleType base="xsd:integer">
                 <xsd:maxExclusive value="14"/>
            </xsd:simpleType>
        </xsd:element>
        <xsd:attribute name="magazineID" type="catalogID"/>
    </xsd:complexType>
</xsd:element>

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