Software Design and Analysis CSCI 2040

Transcription

1 Software Design and Analysis CSCI 2040

2 Introduce a logical architecture using layers Illustrate the logical architecture with UML Package Diagrams 2

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4 Where the class Register should be? 4

5 Where class Register should be? Domain Package 5

6 The logical architecture is the large-scale organization of the software classes into: packages (or namespaces), subsystems, and layers. A layer is a very coarse-grained grouping of classes, packages, or subsystems that has cohesive responsibility for a major aspect of the system. Also, layers are organized such that "higher layers (such as the UI layer) call upon services of "lower" layers, but not normally vice versa. 6

7 User Interface - the means by which the user and a computer system interact Domain Objects application and business logic software objects representing domain concepts that fulfill application requirements, such as calculating a sale total (e.g., a software class Sale). Technical Services general purpose objects and subsystems that provide supporting technical services, such as interfacing with a database or error logging. These services are usually application-independent and reusable across several systems. 7

8 Which layer is Paypal? 8

9 Which layer is Paypal? Technical Services 9

10 Which layer is the Oracle database? 10

11 Which layer is the Oracle database? Technical Services 11

12 Which layer is ebay web interface? 12

13 Which layer is ebay web interface? User Interface 13

14 A logical architecture does not have to be organized in layers, but it is very common: Especially for large and complex systems (e.g., banks) 14

15 A UML package represents a namespace. Dependency is represented with dependency line. 15

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17 Organize the large-scale logical structure of a system into discrete layers of distinct, related responsibilities, with a clean, cohesive separation of concerns such that the "lower" layers are low-level and general services, and the higher layers are more application specific. Collaboration and coupling is from higher to lower layers; lower-to-higher layer coupling is avoided. 17

18 The layers of an architecture are said to represent the vertical slices. While partitions represent a horizontal division of subsystems of a layer. 18

19 // --- UI Layer com.mycompany.nextgen.ui.swing com.mycompany.nextgen.ui.web // --- DOMAIN Layer // packages specific to the NextGen project com.mycompany.nextgen.domain.sales com.mycompany.nextgen.domain.payments // --- TECHNICAL SERVICES Layer // our home-grown persistence (database) access layer com.mycompany.service.persistence 19

20 There are UML tools to reverse-engineer package diagrams from code. A great use for a UML CASE tool is to reverseengineer the source code and generate a package diagram automatically.. 20

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23 The messages sent from the UI layer to the domain layer will be the messages illustrated on the Sequence D., such as enteritem. 23

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25 A domain model can easily grow large enough it is desirable to factor it into packages of strongly related concepts, different people can do domain analysis within different sub-domains. 25

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27 Register class is part of Core Elements package. 27

28 A class shown in a foreign package may have new associations, but must otherwise remain unchanged. Use :: symbol to indicate it 28

29 If a model element is dependent on another, the dependency may be shown with a dependency relationship with an arrowed line. For example, if a package references an element owned by another, a dependency exists. 29

30 At times, it is inconvenient to draw a package diagram, but still desirable to indicate the package that the elements are a member of. In this situation, include a note (dog-eared note) on the diagram. 30

31 To partition the domain model into packages, place elements together that: are in the same subject area closely related by concept or purpose are in a class hierarchy together participate in the same use cases are strongly associated. 31

32 A Core/Misc package is useful to own widely shared concepts or those without an obvious home. In later references, the package name will be abbreviated to Core. 32

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39 As an extreme case, if a widely used utility package such as com.foo.util changed frequently, many things could break. 39

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42 One way to increase package stability is to reduce its dependency on concrete classes in other packages. 42

43 We can reduce the coupling to this concrete package by using a factory object (pattern) that creates the instances, but whose create methods return objects declared in terms of interfaces rather than classes. 43

44 If a group of packages have cyclic dependency then they may need to be treated as one larger package in terms of a release unit. Break the cycle with an interface. 44

45 Alternate UML approaches to showing packages structure, using UML path names, or the circle-cross symbol. 45

46 Why are package diagram useful in practice? How to break cyclic dependencies in package diagrams? Which packages should be the most stable? What are the alternative approaches to show package structure? Software Design and Analysis CSCI

47 Review Slides. Read Chapter 31 about package diagrams Applying UML and Patterns, Craig Larman Software Design and Analysis CSCI