The group Element
The BizTalk group element is similar to the group element of the W3C schema, but unlike the group element defined in the W3C standard, the BizTalk group element cannot be a child element of the schema element. This means that you cannot have document scope group elements. A group element can be used only to group elements within an element declaration-for example, within an ElementType declaration. One of the most useful features of the group element is that it can be used to define a sequence for the child elements of an element.
The group element contains element child elements. The sequence of the child elements can be specified by using the group element's order attribute. If the order attribute is set to one, there can only be one instance of each element in the group. The one value is equivalent to the pipe (|) symbol in a DTD. When the order attribute is set to seq, the elements must appear in the order in which they are declared. Using the seq value is the same as using parentheses and commas in a DTD. The many value indicates that the child elements can appear in any order. The minOccurs and maxOccurs attributes work the same as their counterparts in the element element. We will look at some examples of groups in the section "The ElementType Element" later in this chapter.