Real Time Information Director User Documentation

RTID Metadata Language
Hewlett-Packard Company 6 529618-002
Director Metadata Is Descriptive
Metadata is data about data. The first important characteristic of the Director metadata
is that it is descriptive: it describes the data without describing how to use it. This
characteristic is in contrast with a procedural language such as XSLT, which specifies an
operation or series of operations to perform on the data. (XSLT is a high-level scripting
language, implemented in XML, whose purpose is to convert XML documents to other
forms.)
Because Director metadata is descriptive rather than procedural, the same metadata can
be used to
• Drive the disassembly of documents for loading into the database
• Drive the assembly of documents from records in the database
• Generate an XML schema that describes the document format
Another advantage of descriptive metadata is that it is concise. If you described the same
SAP IDoc using Director metadata and XSLT Style Sheets, the metadata would be about
a tenth the size of the corresponding style sheet, and the style sheet would map the
document in only one direction: document to database, or database to document, but not
both. (This size comparison isn’t just a guess but comes from experience on the HP iHub
project.)
Director Metadata Is Polymorphic
The second important characteristic of the Director metadata is that it is polymorphic.
Polymorphic means characterized by many forms or patterns. Each metadata class
represents a common pattern and has attributes specific to that pattern.
Here’s a popular example of polymorphism:
• Circle and Rectangle are two different classes of Shape.
• A Circle has a defining attribute called diameter.
• A Rectangle has defining attributes called length and width.
Polymorphism gives you the flexibility to represent different patterns economically.
When creating the metadata for a particular type of document, you specify only the
attributes applicable to the pattern at hand. A superclass specifies the common
characteristics of a group of document types.
Polymorphism also makes it easy to evolve metadata as new circumstances arise. New
document definitions can usually be derived from existing metadata classes.
New metadata classes can be added to solve new problems.