well model the requirement that a system must check
whether a buyer have enough money in his back ac-
count before making a purchase in an on-line or phys-
ical store; and modality permissible can be applied to
specify a rule that a bank may check (it is permissi-
ble that bank checks) credit history of a client before
issuing a loan. More on the definition and a Kripke-
style possible world semantics for SDL can be found
in (McNamara, 2006).
The theory of normative positions was originally
inspired by analytical study of law and originated in
the works of Stig Kanger (Kanger, 1972; Kanger,
1985), Ingmar P¨orn (P¨orn, 1970; P¨orn, 1977), and
Lars Lindahl (Lindahl, 1977; Lindahl, 1994). The
Kanger- Lindahl theory is characterized by attempts
to apply modal logic – mainly standard deontic logic,
the field of logic concerned with obligations and per-
missions – and the logic of action and agency to the
concepts of legal and normative relations which Wes-
ley Newcomb Hohfeld (1879–1918), an American ju-
rist, had regarded to as the fundamental legal concep-
tions of jurisprudence (Hohfeld, 1964). These nor-
mative relations are alternatively referred to as nor-
mative positions that take the forms of obligations,
permissions, duties, and rights of agents of a com-
munity, society or some other form of organization.
By agents here we mean humans, machines, or both.
The Kanger-Lindahl theory also embraces the formal
representation of more complex normative positions
such as entitlement, authorization and responsibility.
Besides the areas of legal knowledge representa-
tion (e.g. representation of laws, regulations, legal
contracts, etc.), where the theory of normative posi-
tions found its initial application, there are also other
areas such as Computer Science, where the theory
contributed much for formal representation of rela-
tions between agents. For example, Jones and Sergot
(Jones and Sergot, 1992; Jones and Sergot, 1993) de-
scribe a modified version of the Kanger-Lindahl the-
ory and attempt to apply it to the problem of access
control and security policies specifications and analy-
sis for databases. In (Jones and Sergot, 1993), authors
illustrate by an example of library regulations for gov-
erning the procedures of loaning books that the use of
formal methods in developing system specifications
have to be taken seriously whenever it is necessary
to analyze an ideal case and an actual one and see
how the actual behavior deviates from that of ideal.
Use of such formal methods as deontic logic can help
in revealing the possibility of violations, i.e. those
deviations that had actually occurred. According to
Jones and Sergot (Jones and Sergot, 1993), the use of
deontic logic will in general allow (i) to reason with
the specifications developed, (ii) to be able to test the
internal consistency of the system specifications as a
whole, and (iii) to use theorem provers to implement
and test different components of the system.
In the works of Kanger, P¨orn, and Lindahl
(Kanger, 1972; Kanger, 1985; P¨orn, 1970; P¨orn,
1977; Lindahl, 1977; Lindahl, 1994), deontic logic
was merged with logic of action and agency to pro-
vide a formal account of complex social interactions
within organizations, which can be related to the tech-
nical context by applying it to the multi-agent envi-
ronment. Theyintroducea so-called relativisedmodal
operator which is designated as E
a
, where a represents
a responsible agent. The approach is partially simi-
lar to that of dynamic logic in the sense that it also
assumes that an action, if performed, should bring
about a certain state of affairs. For example, expres-
sion [a]A would mean that after performing action a
it is necessarily the case that A holds. In other words,
a must bring about A. Analogously, haiA means that
after performing action a it is possibly the case that A
holds, or a might bring about A.
However, in the theory of normative positions all
actions are associated with their respective responsi-
ble agents which makes the semantics comparatively
more expressive. When modeling business systems
using this theory we now have to deal with the ele-
ment of agent’s responsibility embedded in the pro-
cess of bringing about new states of affairs. The over-
all concept is formalized by
E
a
A, (1)
which is read as “agent a sees to it that A is the case”
or similarly “agent a brings it about that A”. It is im-
portant to note that actions in this case represent a re-
lationship between agents and the state of affairs that
these agents bring about.
The following expressions are properties for the
action operator. The first axiom schema implies that
the action operator is a success operator:
⊢ E
a
A → A. (2)
It is read as: if agent a brings it about that A then A
is indeed the case. The second property represents a
rule of inference:
I f ⊢ A ↔ B then ⊢ (E
a
A ↔ E
a
B). (3)
Although the approach of combination of deontic
logic with action logic is reminiscent of that of dy-
namic logic by its rules and operators, the theory of
normative positions provides higher expressivity in a
way that, unlike in dynamic logic: (i) by using op-
erator E
a
A one can express different atomic positions
agent a can be in with respect to a particular state of
affairs A; and (ii) using E
a
operator gives another im-
portant advantage, namely, one can also formalise a
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