SEKE 2012 Proceedings - Knowledge Systems Institute

the National Aeronautics and Space Administration (NASA).
The Framework for Interdisciplinary Design Optim ization
(FIDO) project [3] investigated the use of a distributed,
heterogeneous computing system to enhance com munication,
apply computer automation, and introduce parallel computing.
A major limitation in FIDO as determ ined by Salas and
Townsend [3] was that it was used for a specific application.
Hence, the sequences of processes become hard t o code a nd
difficult to m odify. The lack of documentation makes FIDO
inaccessible for the use of researche rs. Salas and Townsend
[3] identified the necessary frameworks during the evaluation
process and the relevant MDO framework requirements were
also briefly described in the paper.
Heitmeyer and Jeffords [4] translated software requirements of
mission critical components for three NASA systems to
specification, which were useful throughout the syste m life
cycle; using a method called Software Cost Reduction (SCR).
The automation process of a flight c ontrol system (AFCS),
must meet strict fault tolerance requirements. Gobbo and Milli
[5] describe formal specification for an analytical redundancy
based fault tolerant flight c ontrol system. The specifications
for the De Havilland DHC-2 general aviation aircraft was
developed using relational a lgebra as t he formal framework.
The requirements are decomposed on a functional basis into
elementary specification a nd then composition operators of
relational algebras are used to build higher level requirements
to develop the whole specifications. Requirem ents can be
interpreted as a relationship among some relevant quantities.
The next section describes the Desc artes specification
language, a form al specification language that is exec utable.
Existing work done on extending the Descartes specification
language to specify complex systems has been described in the
next section.
III.
THE DESCARTES SPECIFICATION LANGUAGE AND THE
EXTENSIONS
The Descartes specification language was designed to be
used throughout the software life cycle. Th e relationship
between the input and the output of a system is fun ctionally
specified using this s pecification language [6]. Descartes
defines the input data and output data and then relates them in
such a way that output data becomes a function of input data.
The data structuring m ethods used with this langua ge are
known as Hoare trees. These Hoare trees use three structuring
methods namely direct product, discriminated union, and
sequence. Direct product is t he default and pr ovides for the
concatenation of sets of elements. Discriminated union is
denoted by a plus sig n (+) suffixed to the node name.
Sequence is indicated by an asterisk (*) suffixed to the node
name. By definition of Hoare trees, a sequence node is
followed by a subnode. A single node ca n accommodate a
sequence of direct product or a sequence of discriminated
union.
Specifying reactive agents using the extended Descartes
specification language was the first attempt made to specify
agents using the Descartes specification language [7] [8].
Extensions to the Descartes specification langua ge for
supporting intelligent software agents were given by Subburaj
and Urban [9]. The new constructs introduced by Subburaj and
Urban capture the requirem ents of intelligent software agents
using the Descartes specification language. Real t ime
semantics can be specified using the Descartes specification
language by the extensions introduced by Sung and Urban [8].
Some of the basic extensions alr eady made to the Descartes
specification language to specify intelligent software agents
[7] that a re also used to specify the aircraft s oftware
components are as follows:
1. estate;
2. astate; and
3. action
The above existing constructs are used in this paper to give a
complete specification of intelligent software agents. In this
paper, extensions to t he Descartes specification language are
based on the concrete BDI architecture proposed by
Wooldridge [2]. The BDI architecture works on the principle
of practical reasoning, wherein the actions to be performed are
decided momentarily in order to achieve the goal. The motive
to specify a nd develop critical aircraft s oftware components
can be realized using the e xtensions made to t he Descartes
specification language. The extended constructs to specify
intelligent software agents based on the BDI architecture
include:
1. belief;
2. belief revision function (brf);
3. option generation function (options); and
4. current options;
1) Belief
In order to represent an a gent’s current environment,
belief has been used. The extensions already m ade to the
Descartes specification language [7] were used to represent
agents environmental states. The reserved word ‘estate’ will
be used to s pecify the different possible environment states.
Based on the agent state and environment state, the next action
will be triggered. The following specification describes the
cruise control to be in one of the two states eith er active or
passive.
agent (CRUISE_CONTROL)_AGENT
CRUISE_CONTROL
‘file’
estate+
ACTIVE
PASSIVE
The agent and environment state information is im portant
while specifying intelligent software agents.
2) Belief revision function
The second extension to Descartes is a new primitive,
“belief revision function”, which uses the inputs given and the
579