Smalltalk and Object Orientation: an Introduction - Free

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of appropriate classes and their interfaces without necessarily having the i nformation to enable them to do this in an appropriate manner for the overall system. For example, little reference is made to the system’s overall functionality when determining class functionality etc. Indeed, some methods provide little more than some vague guidelines and anecdotal heuristics. In contrast, fusion explicitly attempts to provide a systematic approach to object -oriented software development. In many ways the fusion method is a mixture of a range of other approaches (indeed the authors of the method acknowledge that there is little that is new in the approach other than the fact that they have put it all together in a single method, for example see Figure 16.1). Booch OMT Fusion Formal Methods Requirements Analysis Figure 16.1: Some of the influences on Fusion As with other OOD methods, fusion is based around the construction of appropriate models that capture different elements of the system as we ll as different knowledge. These models are built up during three distinct phases. The analysis phase, the design phase and the implementation phase: • The analysis phase produces analysis models which provide a description of the high level constraints from which the design models are developed. • The design phase produces a set of models that describe how the system behaves in terms of a collection of interacting objects. • The implementation phase describes how to map the design models onto implementation language constructs. Within each phase a set of detailed steps attempts to guide the developer through the fusion process. These steps include checks to ensure the consistency and completeness of the emerging design. In addition the output of one step acts as the input for the next. Fusion's greatest weakness is its complexity - it really requires the use of a sophisticated CASE tool. Without such a tool it is almost impossible to produce a consistent and complete design. 16.9 Summary In this chapter we have reviewed a number of OO analysis and design methods as well as the Unified Modeling Language. We have briefly considered what each offers as well as their strengths and weaknesses. It should be noted that a problem encountered with all these systems is th at during the design process it is often difficult to identify commonalities between classes at the implementation level. This means that during any implementation phase, experienced OO technicians should be looking for situations in which they can move implementation level components up in any class hierarchy. This can greatly increase the amount of reuse within a software system. This may then lead to the introduction of new abstract classes whose role is to contain the common code. The problem with t his is that the implemented class hierarchy no longer reflects the design class hierarchy. It is therefore necessary to have a free flow of information from the implementation phase to the design phase and vice versa in an object oriented project. 136
17. The Unified Modeling Language 17.1 Introduction The Unified Modeling Language (or UML for short) is part of a development being carried out to merge the concepts in the Booch, Objectory and OMT methods [Booch and Rumbaugh 1995, Booch et al 1996]. This effort has bee n termed the unification or the Unified Method. The method is still under development (and has taken a much lower profile recently) however the notation underlying this method is nearing completion. This notation has now become the focus of Booch, Rumbaugh and Jacobsons’ current work and is receiving a great deal of interest. For example, Microsoft Corporation, Hewlett Packard, Oracle, Texas Instruments have all endorsed the UML. The UML is a third generation object -oriented modeling language [Rational 1996] which adapts and extends the published notations used in the works of Booch, Rumbaugh and Jacobson [Booch 1994, Rumbaugh et al 1991, Jacobson et al 1992] as well as being influenced by many others (such as Fusion [Coleman et al 1994], Harel’s statecharts [Harel et al 1987; Harel 1988] and CORBA [Ben -Natan 1995], see Figure 17.1). It is intended that the UML will form a single, common, widely usable modeling language for a range of object oriented design methods (includ ing Booch, Objectory and OMT). It is also intended that it should be applicable in a wide range of applications and domains. Therefore it should be equally applicable to client -server applications as it is to real -time control applications. OMT Booch Objectory Fusion UML Corba, OLE/ COM Harel Java Applets Figure 17.1: The influences on the UML notation Part of the justifications for this is that different organizations, applications and domains require (and use) different design methods. In many cases organizations have developed their own methods or have modified other methods through experience. In some cases different parts of the same organizations may use different methods. The result is that the notation used acts as a language in which ideas represented in part (or all) of the design are expressed and communicated. For example, the production of shrink wrapped, off the shelf software, is different from the creation of one off bespoke software. However both activities may be carried out by a software company. Such an organization may well wish to exchange ideas, designs or parts of designs amongst its various departments or operational units. This kind of exchange relies on the availability of a common language - UML provides such a language. At present the UML is in draft form [Booch et al 1996], however it is being presented to the OMG (Object Management Group) in the hope that it will be accepted as a standard (this is an on going process and is part of the OMG’s call for information on obje ct-oriented methods). For the latest information on the UML (as well as any other developments on the unification front) see the Rational Software Corporation’s web site (http://www.rational.com). This chapter provides a brief introduction to the UML but o mits many of the details. For further information on the UML please see version 1.0 of the UML documentation set. There is also a series of books on the UML including a Reference Manual, a User Guide as well as a process book (which at the time of writing were still in the pipe line) that should be referenced for more information. 137
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Smalltalk and Object Orientation: A
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Chapter 7: Smalltalk Constructs Thi
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The user interface construction fac
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Preface 1. INTRODUCTION TO OBJECT O
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12.5 A CLASS SIDE METHOD...........
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27.3 VISUALWORKS WINDOW PAINTING TO
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Part One Introduction to Object Ori
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interfaces between different parts
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een to ease the transition from one
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encapsulation. Attempting to introd
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is a controversial subject which is
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will become second nature to many o
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or return something. It has since b
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defining the behavior of different
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In time most developers start to ac
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2.4.3.4 Smalltalk environments are
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3. Constructing an Object Oriented
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Wash wipe switch Wiper motor Relay
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Point 2 above is more complicated.
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services working? working? working?
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Part Two The Smalltalk Language 42
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other systems. As the browsers, ins
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VisualAge (a version of Smalltalk w
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4.5.2 The VisualWorks Launcher and
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Class categories. These are group s
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5. A Little Smalltalk 5.1 Introduct
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Notifiers can be displayed under a
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These concepts of messages, receive
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Select the “Debug” option. This
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6. Smalltalk Building Blocks 6.1 In
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6.3.1 Class definitions In Smalltal
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Object Class1 Class 2 method search
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“Now calculate y “ y := x * 23.
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7. Smalltalk Constructs 7.1 Introdu
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They are more efficient for storage
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7.5.3 true, false and nil variables
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anArray at: 1 max: 10. This will tr
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Figure 8.1: Defining a new class 8.
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this convention at the moment, howe
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9. Control and Iteration 9.1 Introd
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9.3.3 Block temporary variables Blo
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control the execution of the method
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22.7.2 The Perform: message The per
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From the scenario that a person mig
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23.4 Self testing An approach, sugg
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24. Smalltalk Style Guidelines 24.1
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24.2.4 Adding variables to system c
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should use a dictionary to hold the
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• A method should only send messa
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Table 24.2: Class message categorie
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25. The Perform and Dependency Mech
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• Inheritance (class to class rel
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You can find the methods which impl
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These messages are sent automatical
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26. The Model-View-Controller Archi
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and wit hdrawals and requests for t
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Figure 26.5: Part of the Controller
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model 4. update 1. balance (view) 0
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displayed. The second component add
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27. Graphical User Interface Constr
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27.3.1 Palette The Palette tool pro
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uild a running user interface from
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names) and the actions for buttons
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Edit button, then the user interfac
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27.11 Visual reuse The aim of visua
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Figure 27.17: Defining the parent c
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important, as these facilities hand
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28.3 The AddressBook class 28.3.1 T
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The aspect methods can then be simp
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the name is in the address book, it
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29.2 The custom view widget 29.2.1
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DrawingView model SmallDraw drawing
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The action of adding a new graphic
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The next method we shall consider i
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In the updating protocol we need to
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The displaying protocol contains th
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30. Memory Management and Garbage C
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30.3.3 PermSpace This is used to ho
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31. Concurrency in Smalltalk 31.1 I
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The Semaphore class provides facili
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Once the process wakes up it can de
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31.4.3 Acknowledgments Acknowledgme
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“There are two kinds of objects i
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Object Object class Collection Coll
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ehavior, but from the point of view
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32.5.5 The whole enchilada Behaviou
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33. The Future for Object Technolog
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solutions are needed which suit the
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scripting and query language to use
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34. Appendix: The Smalltalk Languag
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A capitalization convention is used
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• marries: is the message selecto
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Array OrderedCollection SortedColle
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[Coleman et al 1994] D. Coleman, P.
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OOPSLA/ECOOP’90, Joint Conference
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