Databases and Systems

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which the parser only parses the production(s) that it is asked to parse. The example
can be modified so that, if you asked for the token “entry”, the parser would only go
through the productions it needs, i.e. “databank” and “entry”, and would not parse
“id_line”, “de_line”, etc..
SRS is a flexible environment in which databank structures can be fully described
and thus in which databanks can easily be added or changed. Nevertheless, in a
system with many databanks, many indices (at least one per data-field of each
databank) have to be created and updated. The link indices add substantially to the
complexity of the maintenance of a SRS system since they manifest
interdependencies between separate databanks. Fortunately, the index building
process is automated. A program runs automatically at frequent intervals to check if a
new version of a databank exists and performs the appropriate actions. The storage
size for indices is relatively small, about 10 to 20% of the size of the actual indexed
databanks.
Querying and Linking
On top of Icarus, a set of programs and C-API (Application Programming Interface)
functions allow the interrogation of the internal Icarus representation which is
superimposed to the real textual structure of databanks. Queries are expressed in the
SRS Query Language which has been especially designed for the interrogation of
interrelated flat file databanks. SRS queries operate on sets of entries or subentries,
belonging to one or more databanks. The sets are combined using logical operators
AND (‘&’), OR (‘|’) and BUTNOT (‘!’), and also two ‘link-operators’ denoted by the
symbols ‘’.
Operands include index searches of the format “[databank(s)-field:value]” where
one or more databanks can be listed. For querying purposes, the sub-entries (e.g.
features of a sequence) of a databank are considered as a separate databank, and can
be included in this list. Queries on subentry databanks result in sets of subentries.
“Field” identifies the indexed field where the search has to be performed. In the case
of multiple databanks, the field must be defined for all databanks. “Value” can be a
string query with wild cards (‘*’ and ‘?’), a regular expression (delimited by two
forward slashes ‘/’ at the beginning and end and using ‘*’, ‘+’, ‘?’, (...), [...], etc.).
Slightly different syntaxes allow numeric range or date queries. Here are some
examples of queries: