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Contents of /openisis/current/doc/IsisIntro.txt

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Mon Mar 8 17:43:12 2004 UTC (17 years, 3 months ago) by dpavlin
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initial import of openisis 0.9.0 vendor drop

1 * what is isis
3 Isis is a simple, yet powerful database system with a large installed
4 base since the 80s. Since it's well suited for bibliographic data,
5 it's commonly used in libraries, and since it's very low cost,
6 especially in those running on a low budget.
8 * introduction to the isis db
10 An isis DB is a list of rows of unspecified structure, each identified
11 by a unique number, the rowid (a.k.a. mfn). Each row is a list of
12 fields, and each field has number (tag) and a string value. Within a
13 row there may be zero, one or more fields with a given tag. While the
14 field's value usually is a textual representation of data in one or
15 the other character encoding (commonly one of the IBM/DOS code pages),
16 it may actually contain arbitrary bytes. This is closely modelled
17 after ISO2709 "Information Interchange Format" (IIF, a.k.a. ANSI/NISO
18 > http://www.niso.org/standards/resources/Z39-2.pdf Z39.2
19 )
21 * subfields
23 There is a convention to encode multiple fields in one by separating
24 them with a '^' followed by one character tagging the subfield. So the
25 field value '^afoo^bbar^bbaz' represents a field having one 'a'
26 subfield with value 'foo' and two 'b' subfields 'bar' and 'baz'. An
27 other separator char may be used, e.g. ASCII character 31 ("Unit
28 Separator") is used in the
29 > http://www.loc.gov/marc/specifications/specrecstruc.html MARC standard.
31 * formatting
33 There is a formatting language, with literal text, field and subfield
34 variables, if-else branches (on field existance) and for loops (over
35 field repetitions) (roughly speaking).
37 * indexing
39 An index is build by converting a row into a list of words (optionally
40 applying formats) and stuffing every word, qualified by the position
41 of it's occurence in the row, into a B+-Tree (which is actually spread
42 to six files). Searching for a word or word prefix is possible with or
43 without qualifying the position (field). Since all fields can be
44 combined into one index, it is usually not necessary (but possible) to
45 set up multiple indexes.
47 * queries
49 A query language allows for combination of word lookups using and, or
50 and not(without) operators. This is very similar to the "Type-1" query of
51 > ftp://ftp.loc.gov/pub/z3950/official/part1.txt Z39.50.
53 * usage
55 While isis lacks most features of RDBMS like complex relations between
56 different entities, it's flexibility comes in handy for many
57 catalogues and directories with highly varying records and one single
58 level of substructure, which today are usually modelled in XML
59 documents rather than table rows. In other words, isis is an ideal
60 storage for many XML applications. The flexible indexing mechanism
61 combines the best of full text searching and structured retrieval.

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