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Schema Mill


This essay does not describe an existing computer program, just one that should exist. This essay is about a suggested student project in Java programming. This essay gives a rough overview of how it might work. I have no source, object, specifications, file layouts or anything else useful to implementing this project. Everything I have prepared to help you is right here.

This project outline is not like the artificial, tidy little problems you are spoon-fed in school, when all the facts you need are included, nothing extraneous is mentioned, the answer is fully specified, along with hints to nudge you toward a single expected canonical solution. This project is much more like the real world of messy problems where it is up to you to fully the define the end point, or a series of ever more difficult versions of this project and research the information yourself to solve them.

Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; or give you any additional materials. I have too many other projects of my own.

Though I am a programmer by profession, I don’t do people’s homework for them. That just robs them of an education.

You have my full permission to implement this project in any way you please and to keep all the profits from your endeavour.

Please do not email me about this project without reading the disclaimer above.

To work with XML (extensible Markup Language) you need a schema to define the desired structure of the document, the field names, how they nest, which can be repeated, what values are legitimate for the fields and attributes…

Java supports two schema scheme XSD (XML Scheme Definition) and RELAX NG via it DOM (Document Object Model) classes.

It is very labour intensive task to compose a schema. There isn’t even decent schema for PAD (Portable Application Description) files or JNLP (Java Network Launching Protocol).

What your program does is read a well-formed example XML file and generates a scheme for it. On first cut it presumes:

The program the displays the schema to the user as a JTree allowing him to modify simple attributes such repeats 0 to N times (which allow specifying optional fields) and the types of data permitted in a field, e.g. the list of legal values, the low-high bounds. We are building an internal model more clever than most existing schemas. Then you hit a GENERATE button and it cranks out schemas for XSD, and possibly RELAX NG, DTD (Document Type Definition) and Schematron.

Since I wrote this, I discovered there are some commercial implementationss of the idea.

To make the project more challenging, add code to import the various types of schema.

PAD 3.01 spec in HTML
PAD 3.01 spec in XML
Stylus Studio: a commercial schema generator

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