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doc/man/create_version.l

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+.\" This is -*-nroff-*-
+.\" XXX standard disclaimer belongs here....
+.\" $Header: /cvsroot/pgsql/doc/man/Attic/create_version.l,v 1.1.1.1 1996/08/18 22:14:22 scrappy Exp $
+.TH "CREATE VERSION" SQL 01/23/93 Postgres95 Postgres95
+.SH NAME
+create version \(em construct a version class 
+.SH SYNOPSIS
+.nf
+\fBcreate version\fP classname1 \fBfrom\fP classname2 [\fB[\fPabstime\fB]\fP]
+.fi
+.SH DESCRIPTION
+.IR "Currently, the versioning facility is not working."
+.PP
+This command creates a version class
+.IR classname1
+which is related
+to its parent class,
+.IR classname2 .
+Initially,
+.IR classname1
+has the same contents as
+.IR classname2.
+As updates to 
+.IR classname1 
+occur, however,
+the content of
+.IR classname1
+diverges from
+.IR classname2.
+On the other hand, any updates to
+.IR classname2
+show transparently through to
+.IR classname1 ,
+unless the instance in question has already been updated in
+.IR classname1 .  
+.PP
+If the optional
+.IR abstime
+clause is specified, then the version is constructed relative to a
+.BR snapshot
+of
+.IR classname2
+as of the time specified.
+.PP
+Postgres uses the query rewrite rule system to ensure that 
+.IR classname1
+is differentially encoded relative to
+.IR classname2.  
+Moreover, 
+.IR classname1
+is automatically constructed to have the same indexes as
+.IR classname2 .
+It is legal to cascade versions arbitrarily, so a tree of versions can
+ultimately result.  The algorithms that control versions are explained
+in [ONG90].
+.SH EXAMPLE
+.nf
+--
+--create a version foobar from a snapshot of
+--barfoo as of January 17, 1990
+--
+create version foobar from barfoo [ "Jan 17 1990" ]
+.fi
+.SH "SEE ALSO"
+create view(l), merge(l). 
+.SH "BUGS"
+Snapshots (i.e., the optional 
+.IR abstime 
+clause) are not implemented in Postgres.