Rdb: Ruby-Nachbau der MWC /rdb-Werkzeuge

man/searchtree.man

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+.TH searchtree "" "" "/rdb Command"
+.PC "Seek a string node in tree table"
+\fBsearchtree [-m[bhirs]] \fItable root goal column1 column2\fR
+.PP
+.II "directory^search"
+.II "tree^search"
+.II PROLOG
+The command
+.B searchtree
+searches
+.I table
+to see if string
+.I root
+in
+.I column1
+is associated with
+.I goal
+in
+.IR column2 .
+It returns
+TRUE to the shell if it find that
+.I root
+is associated with
+.IR goal ,
+or FALSE if it is not.
+.PP
+.I goal
+may be within
+.IR table ,
+in which case the COHERENT command
+.B grep
+can also find it;
+.BR searchtree ,
+however, will also see if
+.I goal
+be reached by a path from
+.IR root .
+.PP
+The options
+.B \-m[bhirs]
+name the fast-access method to use.
+The default is sequential (\fB\-ms\fR).
+See the entry for the command
+.B search
+for a full description of each method of searching.
+.PP
+.B searchtree
+is a breadth-first search that uses the
+.B search
+fast-access methods to find all of the children at each level of a tree.
+This is the kind of search often done in artificial intelligence programs.
+However,
+.B searchtree
+stores its data in a temporary file rather than in memory,
+so that it will work on very large data bases.
+.PP
+Because
+.B searchtree
+is a shell script, you can modify it to serve many kinds of searches.
+For example, you can add a message like
+.I yes/no
+or
+.IR true/false .
+You can also add shell code to print out a path.
+You might want to use heuristics to guide the search at each
+level, and side effects to update data or print messages along the way.
+.PP
+This kind of searching is also used by the PROLOG language.
+.BR searchtree ,
+however, differs from PROLOG in two significant respects.
+First, PROLOG must have its data base in memory, which
+limits the size of the database it can handle.
+Second, PROLOG uses depth-first searching, which requires it to backtrack.
+.SH Example
+Consider the tree represented by table
+.BR isa ,
+as follows:
+.DM
+Name    Isa
+----    ---
+barbara human
+bill    human
+evan    human
+rod     human
+human   primate
+primate mammal
+cat     mammal
+dog     mammal
+mammal  animal
+bird    animal
+fish    animal
+animal  lifeform
+plant   lifeform
+.DE
+.PP
+Remember that all trees, in fact all graphs, can be listed
+as tables when the nodes (vertices)
+that are connected by a line (arcs) that is on each row.
+A directional graph is handled by having one column be
+.B From
+and another be
+.BR To .
+.PP
+The following command uses
+.B searchtree
+to examine table
+.B isa
+to see if entity
+.B rod
+in column
+.B Name
+is of type
+.B lifeform
+as given in column
+.BR Isa :
+.DM
+	searchtree isa rod lifeform Name Isa ; echo $?
+.DE
+.PP
+The command
+.B "echo $?"
+prints the value returned by
+.BR searchtree .
+In this case, you see `0' (or FALSE), because
+.B rod
+is not a
+.BR lifeform ;
+rather it (or he) is a
+.BR human .
+.PP
+Because
+.B searchtree
+returns only a status code, you can use it as a test condition.
+Your shell program could have a statement like this:
+.DM
+	prompt "What is your name: "
+	read NAME
+	if searchtree isa $NAME lifeform Name Isa
+	then
+        	echo "So, I am talking to a lifeform."
+	else
+        	echo "So, I am talking to another machine."
+	fi
+.DE
+.PP
+The following gives an sample exchange with this script; text in \fBbold\fR
+gives what the user types:
+.DM
+	What is your name: \fBrod\fP
+	So, I am talking to a lifeform.
+.DE
+.PP
+The result of the search of the tree was tested by the
+.B if
+statement, and used to decide which message to print.
+.SH "See Also"
+.B
+search
+.R
+.SH Notes
+.II COHware
+If you wish to experiment with PROLOG, volume 2 of
+.B COHware
+includes the source code to a PROLOG interpreter.
+.SO searchtree