.TH ev 7
.SH NAME
ev \- PQ IRDB database system
.SH DESCRIPTION
\fIEv\fP is a simple database system used for
.IR pq (1)
Implicit Relational Database (IRDB) directory queries. 
An \fIev\fP database consists of a data file, a proto file describing the 
contents of the data file and optional index files for efficient 
database queries.
The arguments to \fIev\fP provide the data and proto file names,
the directory containing the index files, and the database separator.
See 
.IR modules (7).
.P
An \fIev\fP data file is a Unicode file composed of newline-terminated
lines.
Each line in the data file represents a database record and contains
delimited, variable-length fields denoting database attributes.
.P
Information describing the database attributes is stored in a proto file and
used to create the index files and to resolve runtime queries.
Lines in the proto file are newline terminated and have
the following tab- or space-separated fields:
.TP 20
attribute name
Name of attribute in the database.
Cannot be the string \fBattribute\fP or contain the equal sign character 
(\fB=\fP).
Must be less than 15 characters.
.TP 
attribute address
Position of the attribute in the data file.
Attributes are counted left to right starting with field 1 and are
separated by a character delimiter.
See 
.IR modules (7).
.TP 
primary length
Length (in bytes) of entries in the \fIprimary index file\fP.
For attributes that use the numeric matching algorithm, the attribute
length must be at least as large as the longest value.
If index files are not used, this is set to a period (\fB.\fP).
.TP 
secondary length
Length (in bytes) of entries in the \fIsecondary index file\fP.
For attributes that use the numeric matching algorithm, the attribute
length must be at least as large as the longest value.
If index files are not used, this is set to a period (\fB.\fP).
.TP 
match
The match flag is a single character representing the matching
algorithm used for this attribute in database queries.
The possible values are listed below under
.IR "Match Type" .
The match flag may be accompanied by zero or more of the
.I "Value Characteristics"
also listed below.
The order of these one-character flags is not significant.
.TP 
multiple
Contains either a period (\fB.\fP), \fBm\fP, or \fBm=\fP\fIx\fP.
Value \fBm\fP denotes a \fImultiple field\fP.
Value
.BI m= x
signifies the database attribute used to distinguish
between the \fImain\fP line in the data file (attribute=\fIx\fP) and 
\fIauxiliary\fP ones (attribute!=\fIx\fP).
There can be at most one attribute with value
.BI m= x
per proto file.
.TP 
default index
Index files are create by 
.IR pqgen (1M)
for those attributes with default index flag equal to \fBi\fP.
Attributes with default index equal to a period (\fB.\fP) can also be used 
to query the database but with worse performance.
Attributes used frequently for database queries should be indexed.
.SS Match Type
.PD 0
.TP
.B e
Exact match.
.TP
.B n 
Numeric match.
.TP
.B p
Prefix match.
.TP
.B s
Exact match unless argument ends with a star
.RB ( * ),
in which case prefix match.
.PD
.SS Value Characteristics
.PD 0
.TP
.B a
Ignore non-alphanumerics.
.TP
.B i
Ignore case.
.TP
.B m
Multiple entry match.
If argument is empty,
.BR 1 " or"
.BR 2 ,
retrieve first, second or third record for
.IR query ,
respectively.
.PD
.P
The order of the attributes as they appear in the proto file is significant.
For database queries with two or more qualifiers, the attribute that 
appears first in the proto file is used to perform the search of the database.
Attributes with index files are preferred.
.P
Index files, created by 
.IR pqgen (1)
using the data and proto files, improve performance of database queries.
Index files are arranged in a multiway tree format to improve
performance and limit the amount of core memory needed.
.P
The C interface to \fIev\fP can be seen in 
.IR pq (2).
.SH FILES
.PD 0
.TP 30
/lib/pq/dispatch
default pq configuration file
.TP
/sys/src/cmd/pq/example/dispatch
sample dispatch file
.PD
.SH SEE ALSO
.IR pq (1),
.IR pqgen (1),
.IR pq (2), 
.IR modules (7).