Deriving Operational Software Specification from System Goals Xin Bai EEL 5881 Course Fall, 2003

Reference Paper “ Deriving Operational Software Specification from System Goals ” November 2002, Proceedings of the tenth ACM SIGSOFT symposium on Foundations of software engineering

Content Introduction Goal-Oriented Elaboration of Requirements Semantics of Operationalization Operationalization Patterns Analysis

Introduction Lots of techniques and tools for specification analysis Algorithmic model checking, Deductive verification etc. Building formal specifications for complex software is not easy Translate natural language statements to some formal language To be elaborated, structured, interrelated and negotiated

Introduction Goal-oriented requirements engineering The use of goals for requirements elicitation, elaboration, organization, specification, analysis, negotiation, assignment, documentation and evolution.

Introduction Goals Objectives the system under consideration must achieve E.g. “ safe transportation ” and “ reverse thrust enabled when wheels pulse on ” Achieving goals require the cooperation of multiple agents (humans, devices or software)

Introduction Goal refinement To decompose a goal into subgoals so that each subgoal requires the cooperation of fewer agents Stops when goals can be assigned as responsibility of single agents

Goal-oriented elaboration of requirements An application model is composed of four submodels: Goal model Object model Agent model Operation model

The goal model The various objectives the system should meet are defined in this model

The goal model Temporal operators

The goal model

A sample

The object model Defines the domain entities, relationships and attributes A sample

The agent model Defines the responsibilities and interfaces of the various agents A sample

The operation model Defines the various services to be provided by agents Domain pre/post conditions Capture the elementary state transitions defined by operation applications in the domain Required pre/post/trigger conditions Capture additional strengthenings to ensure that the goals are met

The operation model A required preconditions Captures a permission to perform the operation when the condition is true A required trigger condition Captures an obligation to perform the operation when the condition becomes true provided the domain precondition is true A required postcondition Captures an additional condition that must hold after any application of the operation

The operation model Difference between domain and required conditions Domain conditions describe what an application of the operation means in the domain without any prescription as to when the operation must be applied and when it may not be applied.

The operation model A sample for domain conditions

The operation model A sample for required conditions

Semantics of operationalization Functional goals need to be operationalized into specifications of services the agents should provide to meet them Operationalization is a process that maps declarative property specifications to operational specifications satisfying them

Semantics of operationalization It takes the form of a set of operations specified by domain and required pre, post- and trigger conditions.

Semantics of operationalization Correctness of goal operationalization Completeness Consistency minimality

Operationalization patterns A pattern-based technique for operationalizing goals, specified in real- time linear temporal logic (RT-LTL), into operations specified by pre-, post- and trigger conditions

Operationalization patterns An operationalization pattern is an abstract AND-operationalization link between a goal specification pattern in RT-LTL and a set of required pre-, trigger and postcondition specification patterns that operationalize the root correctly.

Operationalization patterns The Immediate Achieve pattern

Operationalization patterns The Bounded Achieve pattern

Operationalization patterns The “ InBetween ” Invariance pattern

A taxonomy of goal patterns

Operationalization patterns In every but very rare cases, the goals match one of the general patterns in the previous taxonomy diagram Not complete, could be enriched with additional goal patterns

Analysis Benefits Abstraction from formal details Completeness assurance Guidance in writing operational specifications Goal mining from operational specifications

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