Information Technology Reference
In-Depth Information
In the above declaration the token Bob belongs to a class named EmployeeClass
that should also be defined by a TELL declaration. Classes can be specialized along
generalizations or ISA hierarchies. For example,
TELL Subject isA Entity
WITH
attribute
subjectName : NameClass
END
means that a Subject is an entity with all entity attributes (as defined in the Entity
Class declaration), plus a name, which is an instance of the Name Class. Note that isA
hierarchies are orthogonal to the classification dimension. In addition, O-Telos pro-
vides operations such as TELL, UNTELL and RETELL, used to extend or modify a
knowledge base, and also RETRIEVE and ASK, which can be used to query it.
4.2
Conceptual Model
A security policy in the SPR consists of the following basic elements:
Objective
,
Guideline
,
Rule,
and
Domain
.
Objectives
The “Objectives” are derived from the organization's strategy towards security. They
express this strategy and the associated security goals in a concrete and precise way.
Guidelines
“Guidelines” are expressed in natural language in the form of 'policy statements'.
They are instructions on activities to be or not to be performed, procedures to be fol-
lowed and decisions to be made. Guidelines in the SPR follow a three level structure:
the first level comprises of abstract guidelines, which come from generic security
policies; the second level guidelines are concrete statements while the third level
guidelines represent implementation options. Each guideline belongs to a category
and is assigned a unique code. This structure facilitates the comparison of security
policies and the assessment of their effectiveness. We may, for example, examine the
completeness of the policy by examining if it provides guidelines covering all catego-
ries.
Rules
Rules in the SPR are represented as formal rules, expressed in first-order logic. The
SPR can check for possible violations of rules automatically, something that cannot
be realized with guidelines. An indicative rule declaration in O-Telos is the following.
TELL StarProperty isA Rule
WITH
attribute, rule
ruledef: $
(exists ag/Agent act1,act2/Activity
o,p/Object
(act1 in BLPpolicy.domain.activity) and
(o in act1.object) and
