Understanding Parametric Indexes


A parametric index is an index that allows retrieval of documents based on the values of parameters. Parametric indexes are the structures that underlie parametric search. Think of a parametric index as an extension to a collection's word index; the Verity engine uses it to identify documents matching the requested parameters.

You can view a parametric index as an n-dimensional “parametric cube” in which each dimension represents a parameter. Parameters are values that can be categorized into useful groupings or sets. For example, Figure 14-1 shows a portion of a three-dimensional version in which the parameters are car color, model year, and location.


Figure 14-1    Parametric Cube



There are individual values or ranges of values for a given parameter. Each parameter as a whole is represented by each dimension of the cube. Each value holds references to the documents that have that meaning for that parameter. For example, in the portion of the cube shown in Figure 14-1, the Color bucket set contains three buckets: Blue, Red, and White. The White value identifies all documents in the collection that relate to white cars.

In this example, a parametric selection for all white cars located in California made in either 2002 or 2003 (the shaded area in Figure 14-1) returns only those documents with field values that satisfy all three criteria.

Parameter values are represented as:

Enumeration—Each unique value is associated with its own value in a parameter. For example, keys for each unique color, such as red, blue, and white, represent separate values.

 

Trees—Values are associated with categories in a taxonomy. The taxonomy specification might be pre-existing, or it can be created dynamically based on fields in the collection or XML data.

 

Attributes—A dynamically-created value, consisting of a name-value pair. The name is dynamically created. The value represents the associated value. A parameter is the set of all attribute values for a specified collection or XML field.

 

For additional information about parametric indexes, see the Verity K2 Parametric Developer Guide.


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