is the photograph descriptor associated with the catalogue entry as well as the

Is the photograph descriptor associated with the

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photograph in the library? is the photograph descriptor associated with the catalogue entry as well as the photograph i.e. if I delete the photograph, do I also delete the catalogue information? 49 Chapter 17 Software reuse The Object Constraint Language The Object Constraint Language (OCL) has been designed to define constraints that are associated with UML models. It is based around the notion of pre and post condition specification common to many formal methods. 50 Chapter 17 Software reuse The OCL description of the Photo Library interface -- The context keyword names the component to which the conditions apply context addItem -- The preconditions specify what must be true before execution of addItem pre : PhotoLibrary.libSize() > 0 PhotoLibrary.retrieve(pid) = null -- The postconditions specify what is true after execution post :libSize () = libSize()@pre + 1 PhotoLibrary.retrieve(pid) = p PhotoLibrary.catEntry(pid) = photodesc context delete pre : PhotoLibrary.retrieve(pid) <> null ; post : PhotoLibrary.retrieve(pid) = null PhotoLibrary.catEntry(pid) = PhotoLibrary.catEntry(pid)@pre PhotoLibrary.libSize() = libSize()@pre 1 51 Chapter 17 Software reuse Photo library conditions As specified, the OCL associated with the Photo Library component states that: There must not be a photograph in the library with the same identifier as the photograph to be entered; The library must exist - assume that creating a library adds a single item to it; Each new entry increases the size of the library by 1; If you retrieve using the same identifier then you get back the photo that you added; If you look up the catalogue using that identifier, then you get back the catalogue entry that you made. 52 Chapter 17 Software reuse Composition trade-offs When composing components, you may find conflicts between functional and non-functional requirements, and conflicts between the need for rapid delivery and system evolution. You need to make decisions such as: What composition of components is effective for delivering the functional requirements? What composition of components allows for future change? What will be the emergent properties of the composed system? 53 Chapter 17 Software reuse Data collection and report generation components 54 Chapter 17 Software reuse
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12/12/2018 10 Key points During the CBSE process, the processes of requirements engineering and system design are interleaved. Component composition is the process of wiring components together to create a system. When composing reusable components, you normally have to write adaptors to reconcile different component interfaces. When choosing compositions, you have to consider required functionality, non-functional requirements and system evolution. 55 Chapter 17 Software reuse
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