XML by Example

This model states that there is at least one reference or one description for

each product (there may be several references or several descriptions).

Also the order is either for a certain quantity or on a time and material

basis, one of the two elements must be present. Figure 10.9 illustrates this

structure.

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Attributes Versus Elements

Figure 10.9: The structure of the new DTD

When resolving these problems, it is important to avoid introducing ambi-

guities in the DTD. The following model would have been ambiguous:

<!ELEMENT lines ((reference+ | (reference+, description+) |

description+),

(quantity | time-material+),price?)+>

It says that a line has ...