Enabling query-by-example, summarization, and clustering

The style.prm file specifies additional data to include in the text indexes to support the following functionality:

Query-by-example – retrieves documents that are similar to a phrase (see “like” for more information).

The text indexes need additional data to support phrases in the query-by-example specification of the like operator. If you use a document in the query-by-example specification, additional data is not required.
Summarization – returns summaries of documents rather than entire documents (see “Using the summary column to summarize documents” for more information).
Clustering – groups documents in result sets by subtopic. See “Using pseudo columns to request clustered result sets” for more information.

You can enable these features for all text indexes by editing the master style.prm file, or you can enable them for an individual text index by editing its style.prm file. Both methods are described below.

Query-by-example and clustering

To use phrases in a query-by-example specification and to use clustering, you must enable the generation of document feature vectors at indexing time. To do this, uncomment the following line in the style.prm file:

$define DOC-FEATURES "TF"

Summarization

To configure the Enhanced Full-Text Search engine for summarization, uncomment one of the following lines that starts with “#$define” in the style.prm file:

# The example below stores the best three sentences of
# the document, but not more than 255 bytes.
#$define DOC-SUMMARIES   "XS MaxSents 3 MaxBytes 255"

# The example below stores the first four sentences of
# the document, but not more than 255 bytes.
#$define DOC-SUMMARIES   "LS MaxSents 4 MaxBytes 255"

# The example below stores the first 150 bytes of
# the document, with whitespace compressed.
#$define DOC-SUMMARIES   "LB MaxBytes 150"

Each of those lines reflects a different level of summarization. You can specify how many bytes of data you want the Enhanced Full-Text Search engine to display, by altering the numbers at the ends of these lines. For example, if you want only the first 233 bytes of data summarized, edit the script to read:

$define DOC-SUMMARIES   "LS MaxSents 4 MaxBytes 233"

The maximum number of bytes displayed is 255. Any number greater than that is truncated to 255.