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7.1.1 Schemas


The Schema is the heart of a Qddb database. Each relation has its own schema that describes the form of the data. You build the schema with an ordinary text editor.

The schema is where you define the structure of tuples by setting out the attributes. Structured attributes exist only for grouping purposes. Non-structured attributes are called leaf attributes. Leaf attributes of a tuple are the containers for data. Both structured and leaf attributes may be expandable, which means that a tuple may have more than one instance. A tuple may have zero instances of any attribute.

Each attribute has a name. In addition, you may give it a type (for a leaf attribute, to restrict the values it may hold), a verbose name (for display purposes), an alias (as a programming convenience), and a convention for splitting values in that attribute into words (for a leaf attribute, to guide word searches).

The schema also lets you define a few storage and format options, such as how the HashTable structure file should be built and the format in which dates are to be input and output.

Herrin Software Development, Inc.