Nicolò Carissimi

in UML 2.0

Summary• what’s behind UML: MDA• UML 2.0 and MDA key concepts

Model Driven Architecture

• a specific software development approach (developed by the Object Managment Group) that shifts the focus from the “code” to the “model” and automatically keeps a relation between them

• a MDA specification consists of:– a Platform Independent Model (PIM)– one or more Platform Specific Models (PSM), each describing how

the base model is implemented on a different middleware platform

• the mapping from a PIM to a PSM is implemented by tools

• system's functionality and behavior are modeled once and only once

UML is the language used for modelling

what’s behind UML: MDA

UML 2.0 and MDA key concepts (1)two MDA’s key concepts guided the improvements over Uml 1 and its

syntax and semantic:

• Automation (of the software development process steps)

– code generation

– verification of software specifications

– ability to execute abstract and incomplete models early in the development cycle

– test cases generation

• Abstraction (the essence of modelling)

the ability to represent a complex system and all its components, with their architecture, behaviour and interactions

UML 2.0 and MDA key concepts (2)improvements over Automation:• increased precision and consistency for complex modelling tools (no

ambiguity)• more formal definition of the meaning of the modelling concepts and

their mutual relationships

improvements over Abstraction:

• improved architecture modeling capabilities (distilled from existing architectural description languages and standards such as Acme, MSC 2000, SDL 2000 and UML-RT) with new diagrams, such as:

– Component Diagrams

– Composite Structure Diagrams

• scalability (the ability to decompose structures at a hierarchical level to an arbitrary level of complexity), with the possibility to refer components’ architecture and interaction defined in separated diagrams

Other UML 2.0 features• complete backward compatibility with UML 1.x

• stronger integration between structure, behaviour and interaction diagrams

• the language has become more complex, so UML 2.0 has been modularized into a set of sublanguages, many of which are independent between each other

Summary• Sequence Diagrams in UML 2.0

• Interaction Frame• Operators

Sequence Diagrams in UML 2.0

two primary improvements:

• “spec-ness”, the ability to specify things, which means less “natural-language notes” and consequently less ambiguity)

• scalability, (here) the ability to reference interactions defined in separated diagrams, thus obtaining a kind of “nested” diagram organization (an interaction is the interplay of messages sent between objects over time for a specific purpose)

Interaction Frame (1)

• What is it? basically, an interaction frame consists of some region of a sequence diagram that is divided into one or more fragments; each frame has an operator and each fragment may have a guard

• How does it realize the aforementioned improvements?• “spec-ness” operators allow to formally express actions which, in UML 1, could only be expressed with the use of notes written in natural language

• scalability diagrams enclosed in a frame can be named and referred in other diagrams

Interaction Frame (2)

op [:arguments]

diagram name | interaction

[ [guard] ]

op (operator):applied to the enclosed interaction(s)(some operators require arguments, such as diagrams names,parameters, constants and guards)

[guard]:a boolean expressionthe interaction is executed accordingto the guard’s value

diagram name:needed if we want to refer to a diagram defined elsewhere

interaction:a (fragment of a) sequence diagram (it cancontain other frames)if we need to enclose more interactions,we’ll separate them with an outlined line(see next slide)

Interaction Frame (3)

op

interaction_1

[guard_1]

…

interaction_n

[guard_n]

this is another example of an interaction frame:

• a set of interactions is divided by an outlined line

• interaction_i is executed if guard_i is true

in the next slides we’ll see the correct syntax for each operator, with its meaning and some examples

Sequence Diagrams: operators (1)sd: <diagram name> (parameters)

it names the diagram contained in the frame

parameters are optional (they can be used if the diagram behaves in different

ways when it’s referred in different occurrences, see this example)

Sequence Diagrams: operators (2)ref

it refers to a diagram defined elsewhere with the sd operatorthe name of the referred diagram is specified in the middle of the frame (with optional parameters closed within round brackets if the referred diagram needs them)

Sequence Diagrams: operators (3)loop minint, maxint [guard]

(think of it as the “for” or “while” statements)

minint: the interaction must loop at least this number of times

maxint (optional): the interaction may not loop more than this number of times

[guard] (optional): after the first minint iterations, the condition is tested

before each additional loop iteration: if the condition is false, then the loop is

abandoned

Sequence Diagrams: operators (3)break

if the selected interaction occurs, the enclosing interaction (in the example below, the one contained by the loop frame) is abandoned

Sequence Diagrams: operators (4)alt

it selects one interaction to be executed from a set of interactionsthe selected interaction follows a true [guard] condition or an [else] condition if none of the guard conditions are true (think of it as the “case” of “if” statements);guards are specified over the lifeline of the object which eventually contains the evaluated variable(s)

Sequence Diagrams: operators (5)opt

the enclosed interaction occurs only if [guard], specified over the lifeline of the object which eventually contains the evaluated variable(s), is true

Sequence Diagrams: operators (6)NOTE: actually the standard gives only a brief description of the following operators and does

not provide an intuitive explanation of their meaning or usage.

assert

the selected interaction must occur exactly in the indicated way, if it doesn’t, you have

an invalid interactionsee http://www.pst.informatik.uni-muenchen.de/personen/stoerrle/V/CSDUML.pdf for some possible interpretations

region

the enclosed interaction is a critical region, no other messages can interleave;

a critical region is needed when a shared resource is updated to prevent the updates from

overlapping and producing inconsistent results;you would typically use this within

parallel interactions

Sequence Diagrams: operators (7)

neg

the enclosed interaction is invalid and can’t occur (it can be used, for example, to model a use case extension which ends with failure)

see http://www.pst.informatik.uni-muenchen.de/personen/stoerrle/V/CSDUML.pdf for some possible interpretations

par

this operator indicates several interactions that may run concurrently (overlapped in time)

seq

partial ordering, “weak”

strict

strict ordering

References• UML 2 Sequence Diagram Overview

http://www.agilemodeling.com/artifacts/sequenceDiagram.htm

by Scott W. Ambler

• UML 2.0: Exploiting Abstration and Automation

http://www.sdtimes.com/opinions/guestview_098.htm

by Brian Selic, IBM Rational Software Canada

• UML 2.0 Incrementally Improves Scalability And Architecture

http://www.elecdesign.com/Articles/Index.cfm?ArticleID=5881

by Bruce Powel Douglas, ED Online

• “Architecting Systems with UML 2.0”

http://www.uml-forum.com/out/pubs/IEEE_SW_Jul03_p57.pdf

by Morgan Björkander and Cris Kobryn, Telelogic

• “UML 2.0 For Dummies”

by Michael Jesse Chonoles and James A. Schardt

Ed. Hungry Minds © 2003

Sequence Diagrams: sd operatorthe diagram Fare_Fase has an input parameter f which makes the sequence diagram

behave in different ways according to it’s value

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