The meaning of “semantics” and “syntax” in XPath

Hi Folks,

The meaning of the word �semantics� is fuzzy in the realm of data interoperability. But in XPath the meaning of �semantics� and �syntax� is clear:

Semantics: the value returned from evaluating the XPath expression.

Syntax: the form of the XPath expression.

Example: Let�s illustrate the use of these terms with an XPath expression for querying this XML document:

<Book>
    <Title>Parsing Techniques</Title>
    <Author>Dick Grune</Author>
    <Author>Ceriel Jacobs</Author>
    <Publisher>Springer</Publisher>
</Book>

Here is the XPath expression:

/Book/Author

The semantics of that XPath expression are the values returned when evaluating the XPath expression on the XML document. These are the values returned:

<Author>Dick Grune</Author>
<Author>Ceriel Jacobs</Author>

That�s the semantics of the XPath expression.

Here is an XPath expression with identical semantics, but different syntax:

/Book/*[self::Author]

Why does the XPath language allow expressions with different syntax and identical semantics?

The rationale, in this example, is that it allows a syntactic distinction to be made between dereferencing a field in a composite object (with the slash operator) and performing an indexed lookup (with the predicate), even though there is no semantic distinction between the two.

Comments?

/Roger