Component vs. Module

Transcription

1 Component vs. Module Component : non-trivial, nearly independent, and replaceable part of a system that fulfills a clear function in the context of a well-defined architecture. Component can be installed and/or instantiated => has a runtime presence. component conforms to and provides the physical realization of a set of interfaces. There is a Component Specification and Implementation. Module: software unit of storage and manipulation. Implements a set of responsibilites Martin Jud Software-Engineering Construction rchitecture / Modules 1 us der Vorlesung chritektur von Jörg Hofstetter HT Luzern Component & Connector View -> ehavior Components & Connector: Execution Units + Shared Data Data flow: Data flow between components. Control flow: ecomes active after Process: What components run in parallel? Deployment: Mapping of components to hardware ToLower «dataflow» Split Merge ToUpper Martin Jud Software-Engineering Construction rchitecture / Modules 2

2 Module View => Structure Logical / Conceptual Structure: The units are abstractions of the systems functional requirements => nalysis-model Decomposition: focusing on is-part-of relation Layer: virtual machines with interfaces Uses structure: focus on depends-on Main «use» Split ToLower ToUpper Merge Config Stdio Capitalize System Martin Jud Software-Engineering Construction rchitecture / Modules 3 Modularisierung The architecture may show detailed decomposition of a module that will be assigned to a single development team. This may be necessary to show how the architecture enables and supports all of the quality attributes that the application must satisfy. The architecture must show the decomposition of a module that will be used by or developed by several design teams. It should be possible to change the implementation of one module without knowledge of the implementation of other modules and without affecting other modules. Martin Jud Software-Engineering Construction rchitecture / Modules 4 dapted from Systems Design by David L. March, DeSales University Webpage

3 Stile der Module View Decomposition is-part-of eziehung divide-and-conquer Generalization is-a eziehung Erweiterung / Interfaces Uses depends-on eziehung chtung: uses = calls (c.f. Layer Relations slide # 23) Layered virtual machines chtung: Layers = Tiers Martin Jud Software-Engineering Construction rchitecture / Modules 5 dapted from Documenting SW rchitectures by Paul Clements et. al. ddison Wesley Coupling & Cohesion High coupling Modules : - Loading platform - Driving unit Low coupling Coupling: the degree to which modules communicate with each other. - How independend are modules? => Minimize Coupling! Cohesion: the degree to which communication takes place among the modules elements. - How close do the elements within a module belong together? => Maximize Cohesion! Martin Jud Software-Engineering Construction rchitecture / Modules 6

4 Coupling What s important: 1. Changes in the body of should not lead to adaptions in other modules. 2. Information Hiding (black-box): Hide any details of the inner construction of from the environment => (1) 3. Simple structure of module dependency => Maintenance becomes easier! Martin Jud Software-Engineering Construction rchitecture / Modules 7 Cohesion Ein Modul soll für eine geschlossene ufgabe zuständig sein nach unterschiedlichen spekten: Funktionsorientiert Datenorientiert Funktionsbibliothek lgorithmus Martin Jud Software-Engineering Construction rchitecture / Modules 8 us der Seminararbeit von Helmut Schmidauer Uni Linz

5 Coupling Cohesion Komplexität Gesamtkomplexität Coupling Cohesion nzahl der Module Martin Jud Software-Engineering Construction rchitecture / Modules 9 us der Seminararbeit von Helmut Schmidauer Uni Linz Minimalität der Schnittstelle möglichst wenige (gar keine) globalen Daten Verlust der Kontrolle wenige exportierte Methoden Methoden des Moduls stark verbunden je mehr exportiert, desto eher falsche Verwendung geringe nzahl von Parametern viele oder komplexe (Klassen / struct) Parameter viele Variationen kompliziertere Verwendung Martin Jud Software-Engineering Construction rchitecture / Modules 10 us der Seminararbeit von Helmut Schmidauer Uni Linz

6 Testbarkeit Korrektheit nachprüfbar ohne Kenntnis des Gesamtsystems hohe indung Testabdeckung wahrscheinlich höher minimale Schnittstelle weniger und einfachere Testfälle Drivers & Stubs - Testrahmen Martin Jud Software-Engineering Construction rchitecture / Modules 11 us der Seminararbeit von Helmut Schmidauer Uni Linz Packages and corresponding Class Relationships Client Service Package ; import.*; public class Client { private Service s;... s.f1 } Package ; public class Service { public f1() {...}; } Martin Jud Software-Engineering Construction rchitecture / Modules 12

7 void cycles in Package Dependencies! Package ; import.*; public class SomeClass { private ClassIn b; } Package ; import.*; public class SomeClass { private ClassIn a; } Martin Jud Software-Engineering Construction rchitecture / Modules 13 How to avoid cycles in package dependencies Martin Jud Software-Engineering Construction rchitecture / Modules 14

8 Modularisierung Nutzen Increases Cohesion Each member of the decomposition should be more cohesive than the aggregate. Decreases Coupling Fine grained modules should depend less on each other than course grained modules. Reduces Fan-Out Fine grained modules often have lower fan-out than course grained modules. Isolates Potential Changes Modules should be used to encapsulate the effects of likely changes. This involves the principle of information hiding. Enables Parallel Development Modules with well defined relationships and interfaces can be developed by separate teams. Martin Jud Software-Engineering Construction rchitecture / Modules 15 dapted from Systems Design by David L. March, DeSales University Webpage Modules Layers Components module is an implementation unit component is a runtime unit. In this figure modules are grouped into layers. Each layer will be developed by a different team. The bold boundary illustrates the modules that participate when the corresponding component is running. Martin Jud Software-Engineering Construction rchitecture / Modules 16 dapted from Systems Design by David L. March, DeSales University Webpage

9 Layered rchitecture User Interface GUI, Windows, Dialog, Reports, HTML, JSP dependency more app. specific usiness Services usiness Objects Workflow, Use Case Realisation, Session State, pp. Controller, Transactions (e.g. Lendook) Entity Objects (e.g. ook) Infrastruture Persistence, Security... Martin Jud Software-Engineering Construction rchitecture / Modules 17 Module View: Vertical Layers -> use-relationship or «use» Key: allowed to use The public facilities in layer are allowed to be used by the software in layer. unit of software is said to use unit if s correctness depends upon a correct implementation of. The higher layers are normaly more abstract. Martin Jud Software-Engineering Construction rchitecture / Modules 18

10 Segmented Layers (Horizontal Partitions) Sometimes layers are divided into segments denoting some finergrained decomposition of the software. Is software in 1 allowed to use software in 2 and 3, or only software in 1? Is software in 2 allowed to use software in 1 and 2 but not 3? May 1, 2, and 3 use each other? => These relations must be spelled out. Martin Jud Software-Engineering Construction rchitecture / Modules 19 No Layers! a: ok a c b: possible, but dangerous b c c: not allowed (no cyclic dependency in layers)! a c C Martin Jud Software-Engineering Construction rchitecture / Modules 20

11 Layer Relations P0 P2 program/class P0 can use program P1 without calling it: e.g. P0 may assume that P1 has initialized a shared device. «uses» «calls» P1 (*) important: the name of the errorhandler is not hard-coded into P1! program/class P1 might call program P2 but not use it: - P2 is an error-handler, whose name is passed to P1 by its client or via some name server (*). - P1 calls P2 when it detects an error of some sort, P1 will usually not care what P2 actually does. Martin Jud Software-Engineering Construction rchitecture / Modules 21 Tiers Layers are very often confused with the tiers in an n-tier client-server architecture, such as shown in the following figure: notice the two-way arrows! Presentation Layer usiness Logic Data Server Often used for: llocation to machines in a distributed environment. Data flow among elements. The presence and utilization of communication channels Martin Jud Software-Engineering Construction rchitecture / Modules 22

12 Layers in UML more details: «uses» «uses» Martin Jud Software-Engineering Construction rchitecture / Modules 23 Example: POS System Overview & Dependencies Presentation Swing ProcessSale Frame Domain Sales Register Sale Pricing Serviceccess Services Factory Payments CreditPayment «interface» ICredituthorization Servicedapter Inventory «interface» IInventorydapter POSRuleEngine POSRuleEngineFacade Taxes «interface» ITaxCalculatordapter Technical Services Persistence DFacade Log4J Jess SOP Martin Jud Software-Engineering Construction rchitecture / Modules 24