Field Selection Table (FST)

The FST is the "brain" of the search engine. While the FDT defines storage, the FST defines access. It tells ABCD which fields should be searchable and how to process them into the Inverted File (Index).

• Location: bases/db_name/data/db_name.fst

An FST entry consists of three parts: Identifier (ID), Indexing Technique (IT), and Extraction Format.

Indexing Techniques (IT)

The Technique determines how the extracted text is split into keys (search terms).

IT	Name	Description	Example Input	Index Entry
0	Full Field	Indexes the entire line as a single phrase.	History of Art	History of Art
1	Subfield	Indexes specific subfields defined in the format.	^aDoe^bJohn	Doe
2	<> Bracket	Indexes only text enclosed in < and >.	History of <Art>	Art
3	// Slashes	Indexes text in /.../ as a phrase, rest as words.	/History of Art/	History of Art
4	Word	Indexes every word individually.	History of Art	History, of, Art
8	Word (Stopword)	Same as 4, but ignores words in a Stopword List (.stw).	History of Art	History, Art

Extraction Format (PFT)

This uses the ISIS Formatting Language to precise exactly what to index.

A. Basic Indexing

• Full Text (Technique 4): Index every word in the Title.
  • Format: v245
• Phrase Indexing (Technique 0): Index the full author name as one string.
  • Format: v100

B. Using Prefixes

To distinguish between an Author "Green" and a Color "Green", use prefixes.

• Technique: 0 (Line) or 1 (Prefix).
• Format: "TI_"v245
• Result: TI_GREEN (Searchable as TI_GREEN).

C. Handling Repeatable Fields (Crucial)

If a field is repeatable (e.g., Tag 70 Authors), using v70 concatenates all authors into one long line. To index them separately, you must use a repeatable group with a line break.

• Incorrect: v70 (Result: SmithJohnsonDoe)
• Correct: (v70/)
• Result:

  Smith
  Johnson
  Doe

  (The FST processes each line as a separate key).

D. Conditional Indexing

You can use logic to decide what to index.

• Example: Index Tag 10 only if the status (Tag 20) is "Active".
  • Format: if v20='Active' then v10 fi

:::warning Re-Indexing Changes to the FST do not take effect immediately. You must run a Full Inverted File Generation (Maintenance Menu) to apply changes to existing records. :::