GTM Requirements
This is the requirements for GTM, the Graphical Topic Maps
Notation, which will eventually become ISO 13250-7.
GTM will consist of two sub-parts, for the time being informally
known as GTM level 0 and GTM level 1. This does
not imply that GTM will be a multi-part standard in the ISO sense of
this term; simply that GTM will define two closely related, but
different, graphical notations. (For more information, see below.)
1. Purpose
GTM is being created to enable the communication of information by
means of graphical models. However, GTM should support the
communication of two different kinds of information, and so there are
two different sets of purposes being served by it:
- GTM should be usable for communicating the contents of a topic
map to students and readers of technical papers. This means that GTM
should effectively be able to express the same information as the
TMDM, but in a visual form. This is the purpose served by GTM
level 0.
- GTM should be usable to communicate the constraints on a Topic
Maps ontology to customers, developers, students, and readers of
technical papers. This means that GTM should effectively be able to
express the same information as TMCL Schema, but in a visual
form. This is the purpose served by GTM level 1.
2. General requirements
The following requirements are goals, which GTM should satisfy:
- GTM must support both of the purposes described above.
- GTM should be easy for humans to read.
- GTM should be easy for humans to write, using either
- a modelling
tool with GTM support,
- a general vector drawing tool, or
- simply
manually on a whiteboard or blackboard.
- GTM models should be compact, and conserve visual real estate.
- The two parts of GTM should be visually consistent; that is,
they should use a common set of shapes.
- The GTM standard should not rely on colour for communicating model
information. That is, if a GTM model is printed in black and white,
no standardized information should be lost.
- A GTM model is not required to display every aspect of the
represented TMDM/TMCL instance. If essential information is omitted,
GTM must specify the shapes to be used as a "shorthand" for the
omitted information. (Note that this applies only to simplifications
such as omitting the type and role types of an association, and is
not a general templating mechanism or support for clustering of
topics.)
- This requirement has been deleted.
- This requirement has been deleted.
- All GTM models must be required to use a consistent set of
shapes to represent the various underlying TMCL and TMDM
constructs. (That is, the shape used to represent, e.g, topic types
should be consistent across all GTM models.) However, GTM should aim
to not constrain visual representations of GTM models any more than
what is necessary for consistency. That is, the constraints on
visual representations should be minimal.
- Requirements on shapes must be specified as minimal requirements
only, to allow users to make extensions to GTM (such as use of
colour and fill patterns) without being incompatible with the
standard.
- GTM must define precisely what is considered to be consistent
with the standard, and what is not. (For example, is rotation of the
shape allowed; is using a fill colour inside the shape allowed, etc
etc)
- This requirement has been deleted.
- GTM must provide some way of visually representing both
information from level 0 and level 1, and the connections between
the two levels.
- GTM must support breaking models up into several diagram in
such a way that it is possible to see how the diagrams fit together
into a single model.
- It must be possible to add textual comments to diagrams.
The following functionality will not be provided by GTM:
- GTM will not define an interchange format for GTM diagrams and
models similar to XMI for UML. (Except in so far as this is
supported by CTM and XTM.)
- Features such as filtering, zooming, and layering will not be
defined by GTM, although tools may well provide these functions, so
long as the resulting models conform to GTM.
- No data model for the visual shapes will be defined.
3. Requirements on GTM level 0
The following are requirements on the part of GTM that is intended
to represent TMDM instances:
- GTM level 0 must be able to represent all item types and
properties in the TMDM.
- GTM level 0 may also define shapes for representing the
type-instance and supertype-subtype association types defined by
TMDM.
- There must be a precise definition of how the shapes in GTM
level 0 map to constructs in the TMDM.
The following are requirements that GTM level 0 will not
attempt to meet:
- GTM level 0 only represents TMDM, and no attempt will be
made to represent any aspects of CTM and XTM beyond those present in
TMDM.
An example of information that could be represented with GTM level
0 is: "Tosca was composed by Puccini" (an association item with two
role items).
Note that since TMCL constraints have a TMDM representation it is
possible to represent these constraints in GTM level 0. This is
considered to be useful for communicating the TMDM representation of
TMCL constraints, but not to be suitable for communicating an
actual set of constraints to customers etc as described under
"Purpose" above. This is why a level 1 is proposed in addition to
level 0.
4. Requirements on GTM level 1
The following are requirements on the part of GTM that is intended
to represent constraints:
- GTM level 1 must be able to express everything that TMCL Schema
can express. That is, it must be possible to generate a TMCL Schema
from a GTM level 1 model.
- GTM level 1 must be conceptually similar to existing modelling
formalisms such as UML, ORM, and ER.
- GTM level 1 must allow a representation of TMCL constraints
that is more compact than the representation of the TMDM form of
these constraints in GTM level 0.
- There must be a precise definition of how the shapes in GTM
level 1 map to constraints in TMCL.
An example of information that could be represented with GTM level
1 is: "every opera must have at least one composer" (a constraint on
the use of the association type with the opera topic type).
5. Editorial requirements
The goal of the editors is to get both level 0 and level 1 into ISO
13250-7 at the same time. However, level 0 depends on TMDM, which is
finished, while level 1 depends on TMCL, which is not. There is
therefore a danger that level 0 could be finished before TMCL is
finished. There is a general understanding that in this case, GTM will
initially be published with only level 0, without waiting for level 1,
and that level 1 will be added later.
