Table of contents

Appendices

1.2 Relationship to XML External Entities

There are a number of differences between XInclude and [XML] or [XML11] external entities which make them complementary technologies.

Processing of external entities (as with the rest of DTDs) occurs at parse time. XInclude operates on information sets and thus is orthogonal to parsing.

Declaration of external entities requires a DTD or internal subset. This places a set of dependencies on inclusion, for instance, the syntax for the DOCTYPE declaration requires that the document element be named - orthogonal to inclusion in many cases. Validating parsers must have a complete content model defined. XInclude is orthogonal to validation and the name of the document element.

External entities provide a level of indirection - the external entity must be declared and named, and separately invoked. XInclude uses direct references. Applications which generate XML output incrementally can benefit from not having to pre-declare inclusions.

Failure to load an external entity is normally a fatal error. XInclude allows the author to provide default content that will be used if the remote resource cannot be loaded.

The syntax for an internal subset is cumbersome to many authors of simple well-formed XML documents. XInclude syntax is based on familiar XML constructs.