DTDinst

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Version 20030619

DTDinst is a program for converting XML DTDs into an XML instance format.

Previous versions of DTDinst could also convert XML DTDs into RELAX NG. This functionality has now migrated into Trang, which now shares the DTDinst code.

The key feature of DTDinst is its handling of parameter entities. It is able to reliably turn parameter entity declarations and references into a variety of higher-level semantic constructs. It can do this even in the presence of arbitrarily deep nesting of parameter entity references within parameter entity declarations. At the same time, it accurately follows XML 1.0 rules on parameter entity expansion, so that any valid XML 1.0 DTD can be handled. If a parameter entity is used in a way that does not correspond to any of the higher-level semantics constructs supported by DTDinst, then references to that parameter entity will be expanded in the DTDinst output.

Getting DTDinst

The DTDinst distribution is available in the download directory. The file is called dtdinst-version.zip. It includes both a JAR file and source code.

You also need to have a Java runtime environment installed on your system.

Running DTDinst

To run DTDinst, use a command of the form:

java -jar dtdinst.jar DTD

The DTD argument can be either a file or a URL.

DTDinst writes an XML representation of the DTD in DTDinst format to the standard output. For example, the command

java -jar dtdinst.jar http://www.w3.org/XML/1998/06/xmlspec-v21.dtd >xmlspec.xml

would write an XML representation of the W3C xmlspec DTD to the file xmlspec.xml.

DTDinst format

The DTDinst format is designed to represent the parameterization of the DTD as fully as possible.

There is a schema for this format in RELAX NG compact syntax; the schema is also available in RELAX NG format.

Each parameter entity declaration is represented by one of the following elements:

modelGroup is used for a parameter entity that represents all or part of the content model of an element (example, DTDinst output)
attributeGroup is used for a parameter entity containing zero or more attribute definitions, which can be referenced in an ATTLIST declaration (example, DTDinst output)
attributeDefault is used for a parameter entity that represents the default value of an attribute (example, DTDinst output)
datatype is used for a parameter entity that represents an attribute type (example, DTDinst output)
enumGroup is used for a parameter entity that contains zero or more enumerated values (example, DTDinst output)
flag is used for a parameter entity with replacement text INCLUDE or IGNORE, which can be used to control a conditional section (example, DTDinst output)
nameSpec is used for a parameter entity that represents the name of an element or attribute (example, DTDinst output)
externalId is used for an external parameter entity that does not fall into any of the above categories (example, DTDinst output)
param is used for an internal parameter entity that does not fall into any of the above categories (example, DTDinst output)
overridden is used for a parameter entity declaration that is overridden by an earlier declaration of the same parameter entity (example, DTDinst output)

The element used to represent a parameter entity reference depends on the element used to represent the declaration of the parameter entity.

If the declaration is represented by a modelGroup, attributeGroup, attributeDefault, datatype, enumGroup, flag or nameSpec element, then the reference will be represented by a modelGroupRef, attributeGroupRef, attributeDefaultRef, datatypeRef, enumGroupRef, flagRef or nameSpecRef element respectively.
If the declaration is represented by externalId and the reference occurs at the declaration level (i.e. at a point where a declaration would be allowed), then the reference will be represented by a externalIdRef element containing the declarations from the external entity.
Otherwise, the reference will be expanded and there will be no indication that a reference was originally used in the DTD.

An XSLT stylesheet is available that converts DTDinst format to RELAX NG. It has many more limitations than the converter builtin to DTDinst, but it may be useful as a basis for XSLT-based processing of DTDinst format.

Sample DTDs

You may find it interesting to experiment with the following XML DTDs which are available online:

Limitations

DTDinst does not attempt to understand the contents of ignored conditional sections: DTDinst format represents the contents of an ignored section as a string. If you wish to preserve information about conditional sections, you should therefore make as many conditional sections as possible be included marked sections rather than ignored marked sections. You can do this by creating a wrapper DTD that declares parameter entities as INCLUDE and then references the real DTD. For example, you might use this wrapper DTD to convert the TEI P4 DTD.

DTDinst does not attempt to understand the contents of parameter entities that are never referenced.

Reporting bugs

Please send bug reports to jjc@thaiopensource.com. Be sure to include a complete DTD for which DTDinst exhibits the bug.

James Clark