Database Management Reference Manual
Introduction to Database Concepts : Database Expressions and Rules
Database Expressions and Rules
Expressions
Database expressions can be of the following types:
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algebraic
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boolean (or logical)
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text
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Element ID
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position
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direction
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orientation
The contents of an expression may contain the standard operator and mathematical functions along with the names of attributes and element identification.
Examples of expressions are:
Real Expression: (XLEN * YLEN * ZLEN * 2)
This expression simply multiplies the three attributes XLEN, YLEN, ZLEN together and then multiplies by two.
The attributes refer to the current element. If attributes of other elements are required then the OF syntax is used.
Boolean expression: (PURP EQ 'HS' AND AREA OF OWNER EQ 1)
The 'OF' keyword makes sure that the AREA attribute is obtained from the owner of the current element rather than the current element itself.
The main uses of expressions are:
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Catalogue parameterisation
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Template parameterisation
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Rules
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Drafting line styles
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User level collections and report
Database expressions are very similar to PML expressions. The major difference is that database expressions may not contain other PML variables or functions. E.g. (XLEN * !MYVAR) is not a valid database expression.
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