.TH CNSTR 6
.SH NAME
cnstr \- Plan B volume constraints and attributes
.SH DESCRIPTION
.PP
The Plan B
.IR bns (4)
program permits the application to mount
at a given mount point those volumes whose names and attributes
match the ones given as arguments, as said in
.IR planb (1).
.PP
Volume attributes can be used as
constraints to determine which ones of the
volumes available for a given mount point are of interest for
the application. A
constraint is a set of values for attributes that refer to
properties of the resource volume. Both volume announces and volume
mount requests carry a constraint used to pair them.
.PP
A constraint is a single argument, field, or string. Its format is a set
of
.IR attr = value
pairs delimited by white space. No space may be around the equal
sign. Also, when using
.IR rc (1),
it is important to quote all the attribute/value pairs together, or they would
become different constraints, and not a single one.
.SH ATTRIBUTES
.PP
By convention, the following attribute names and values are used through the system, 
This convention should be followed or users will not know how to request a given
property for a resource. Of course, this is highly regional and the version shown here
corresponds to customs at URJC.
.LP
.ta +10, +10, +10, +10
.br
.di x
				\ka
.br
.di
.in \nau
.ti0
	Attribute	Name	Values	Description
.in \nau
.ti0
	Type	type		Type for the resource serviced.
Usually corresponds to the data format for the device involved.
.ti0
			text	text without null characters.
.ti0
			bin	program binary
.ti0
			dir	file hiearchy
.ti0
			pcm	audio PCM data.
.ti0
			mp3	MPEG 2 layer 3 data.
.ti0
	Arch	arch		Architecture for the resource. Commonly
used for
.B bin
types.
.ti0
			386	Plan B (or Plan 9), 386.
.ti0
			arm	Plan B (or Plan 9), ARM.
.ti0
			lin	Linux on 386 PC.
.ti0
			win	Windows on 386 PC.
.ti0
			sym	Symbian, native.
.ti0
	UI	gui		User interface service. Identifies the
type of device available.
.ti0
			big	Large graphics device
.ti0
			small	Small graphics device
.ti0
			txt	Text only device
.ti0
	location	loc		Name
used to represent the location of the volume. Corresponds to a directory in
.B /where
that keeps context for the given location.
.ti0
.ti0
	user	user		Identifier
used for
the user, to identify volumes of interest for (or owned by) a particular user.
.ti0
	machine	sys		Identifier
used for
the machine, to identify volumes served by that particular machine.
.ti0
	domain	dom		Identifier
used for
the adminstrative domain, to locate volumes within domains.
.ti0
	Con	net		Connection. Specifies the quality of
the link used to reach the volume.
.ti0
			ok	Latency seems to be ok.
.ti0
			bad	Latency is a bad one.
.LP
Other types and values not documented here may exist, although those
commonly used should be described above. The convention is that attributes
not listed here are not standard at URJC.
.SH "SEE ALSO"
.IR planb  (1),
.IR namespace.planb (4),
.IR bns (8),
.IR mount (2).