4.45 Elementary Method "State Transition Modeling" (STM)

#### 1 Identification/Definition of the Method

/Martin, 1987/ pp. 298-305

#### 2 Brief Characteristic of the Method

Objective and Purpose

Method "State Transition Modeling"(STM) is used to model functions and realtime processes. Based on a description via finite automatons, a precise definition of the required system behavior is to be realized.

Means of Representation

Means to represent STM are the state transition diagrams (STD's).

In this connection there exist various notation forms - diagrams, tables, matrices, fence diagrams - which all model the same subject, though.

Fence Diagrams have the advantage to allow a better overview in case of complex diagrams.

Apart from these graphic representations of STD, there are several similar in content, table-oriented notations with special characteristics (also see /Hatley, 1987/ (pp. 87-89)).

To represent several-also nested-communicating automata the graphical representation according to /Harel, 1987/ (pp. 232-262) is well suited.

Operational Sequence

The procedure abstracts a number of states (semantically disjointed) for the function to be modeled or respectively for the realtime process, then it defines appropriate state transitions and specifies the corresponding events ("inputs") and accompanying actions ("outputs"). The automatons thus designed are deterministic and can be analyzed for formal consistency characteristics.

In the case where the automaton to be described is too large and thus not sufficiently concise, /Martin, 1987/ (p. 298, 299) recommends a decomposition into several connected or nested subautomata. Such communicating automata (also see /Harel, 1987/ (pp. 232-262)) enable a transparent design of extensive systems and complex interfaces.

#### 3 Limits of the Methods Application

The basic method is to be applied if complex situations have to be taken into consideration in connection with the execution of a function.

#### 4 Specification of the Methods Allocation

No. Activity Description
4.1 SD3.3 - Definition of Requirements for the Functionality The basic method is applied for the individual descriptions of SW Unit functions. The individual states of the function as well as its various operation modes are identified. It is specified in which states which (sub) functions must be executed, and what is the reason for the initiation of the status transition.

By applying the basic method STM, subproduct Technical Requirements.Overall Function of Element is partially covered, i. e. the contents "States" and "Operation Modes" are covered.

4.2 SD4.1 - SW Architecture Design After being prepared by PIM - Process Interaction Modeling, all individual SW Unit processes are completely specified by means of the basic method and by taking into consideration their communication. In this connection, the Sequence Charts from the PIM and the functional structure from the Technical Requirements are taken into consideration.

Together with PIM, the basic method covers subproduct SW Architecture.Individual Descriptions to that extent as process states and communication structures are affected.

#### 5 Interfaces

No. Interface Observation Information in Annex 1
5.1 STM-CFM The control specification CSPEC must be realized by means of a state transition diagram or by an equivalent means of representation. The state transition diagram is integrated into the Control Flow Modeling. 4.14 Interface CFM-STM
5.2 STM-PCODE The formulation by Pseudocode has to reflect the behavior specified for the individual processes by the state diagrams. 4.17 Interface PCODE-STM
5.3 STM-PIM The signals or respectively the data between processes according to PIM are allocated to individual states and transitions according to STM. 4.18 Interface PIM-STM

#### 6 Further Literature

/Harel, 1987/ Statecharts: A Visual Formalism for Complex Systems
/Hatley, 1987/ Strategies for Real-Time System Specification
/Martin, 1987/ Diagramming Standards for Analysts & Programmers

#### 7 Functional Tool Requirements

SSD04 - Supporting Process Modeling

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