©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 1 Software Requirements l Deskripsi dan spesifikasi sistem.

Presentasi berjudul: "©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 1 Software Requirements l Deskripsi dan spesifikasi sistem."— Transcript presentasi:

1 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 1 Software Requirements l Deskripsi dan spesifikasi sistem

2 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 2 Objectives l Menjelaskan konsep kebutuhan user dan kebutuhan sistem l Mendeskripsikan kebutuhan fungsional dan non- fungsional l Menjelaskan dua teknik dalam mendeskripsikan kebutuhan sistem l Menjelaskan bagaimana kebutuhan software diorganisasikan dalam dokumen kebutuhan

3 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 3 Topics covered l Functional and non-functional requirements l User requirements l System requirements l The software requirements document

4 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 4 Requirements engineering l Proses penentuan service yang dibutuhkan customer dalam sebuah sistem dan penentuan batasan lingkungan pengoperasian dan pengembangan sistem l The requirements themselves are the descriptions of the system services and constraints that are generated during the requirements engineering process

5 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 5 What is a requirement? l Cakupan definisi requirement cukup luas, dapat berupa pernyataan abstrak secara umum dari layanan atau batasan sistem, dapat juga berupa spesifikasi fungsional matematis yang lebih rinci l Tidak dapat dipungkiri bahwa requirements memiliki fungsi ganda : Sebagai dasar untuk penawaran kontrak – itulah sebabnya requirement haruslah diintepretasikan secara terbuka Sebagai dasar untuk pembuatan kontrak itu sendiri – itulah sebabnya requirement harus didefinisikan secara detail Kedua pernyataan diatas dapat disebut sebagai requirements

6 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 6 Requirements abstraction (Davis)

7 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 7 Types of requirement l User requirements Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers l System requirements A structured document setting out detailed descriptions of the system services. Written as a contract between client and contractor l Software specification A detailed software description which can serve as a basis for a design or implementation. Written for developers

8 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 8 Definitions and specifications

9 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 9 Requirements readers

10 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 10 Functional and non-functional requirements l Functional requirements Pernyataan mengenai kebutuhan layanan sistem yang harus disediakan, bagamana sistem akan bereaksi terhadap masukan tertentu dan bagaimana mestinya sistem beraksi pada situasi tertentu. l Non-functional requirements Batasan dari layanan atau fungsi yang ditawarkan sistem, misalnya batasan waktu, btasan proses pengembangan, standard dan lain-lain l Domain requirements Requirements yang berasal dari domain aplikasi sistem yang mencerminkan karakteristik domain

11 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 11 Functional requirements l Menjelaskan fungsionalitas atau layanan yang disediakan sistem l Bergantung pada tipe software, keinginan users dan tipe sistem dimana software tersebut digunakan l Functional user requirements bisa jadi pernyataan secara umum mengenai bagaimana sistem akan bekerja akan tetapi functional system requirements harus mampu mendifinisikan layanan sistem secara lebih rinci.

12 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 12 Examples of functional requirements l The user shall be able to search either all of the initial set of databases or select a subset from it. l The system shall provide appropriate viewers for the user to read documents in the document store. l Every order shall be allocated a unique identifier (ORDER_ID) which the user shall be able to copy to the account’s permanent storage area.

13 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 13 Requirements imprecision (ketidak sesuaian penentuan requirement) l Masalah akan muncul saat requirements tidak dinyatakan dengan tepat l Requirements yang Ambiguous kemungkinan akan diinterpretasikan dengan sudut pandang yang berbeda oleh developers dan user l Consider the term ‘appropriate viewers’ User intention - special purpose viewer for each different document type Developer interpretation - Provide a text viewer that shows the contents of the document

14 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 14 Requirements completeness and consistency l Pada prinsipnya requirements haruslah lengkap dan konsisten l Lengkap dalam arti : They should include descriptions of all facilities required l Konsisten dalam arti : There should be no conflicts or contradictions in the descriptions of the system facilities l Namun pada prakteknya, sangatlah sulit menghasilkan dokumen requirement yang lengkap dan konsisten

15 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 15 Non-functional requirements l Mendefinisikan properti dan batasan sistem (misalnya reliability, response time dan storage requirements). Batasan dapt berupa kemampuan perangkat I/O, representasi sistem dan lain-lain l Process requirements may also be specified mandating a particular CASE system, programming language or development method l Non-functional requirements may be more critical than functional requirements. If these are not met, the system is useless

16 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 16 Non-functional classifications l Product requirements Requirements yang menentukan bahwa delivered product harus memenuhi syarat tertentu misal execution speed, reliability, dan lain- lain. l Organisational requirements Requirements yang terkait dengan konsekuensi kebijakan dan prosedur organisasi misalnya standar proses yang digunakan, implementasi requirements, dll. l External requirements Requirements yang muncul dari faktor-faktor external sistem dan proses pengembangan misalnya interoperability requirements, legislative requirements, dll.

17 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 17 Non-functional requirement types

18 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 18 Non-functional requirements examples l Product requirement It shall be possible for all necessary communication between the APSE and the user to be expressed in the standard Ada character set l Organisational requirement The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP-STAN-95 l External requirement The system shall not disclose any personal information about customers apart from their name and reference number to the operators of the system

19 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 19 Goals and requirements l Non-functional requirements mungkin terlalu sulit untuk dinyatakan dengan tepat dan requirement yang salahpun kemungkinan sulit sekali untuk diverifikasi. l Goal A general intention of the user such as ease of use l Verifiable non-functional requirement Pernyataan yang menggunakan sejumlah ukuran yang dapat ditest secara obyektif l Goals are helpful to developers as they convey the intentions of the system users

20 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 20 Examples l A system goal The system should be easy to use by experienced controllers and should be organised in such a way that user errors are minimised. l A verifiable non-functional requirement Experienced controllers shall be able to use all the system functions after a total of two hours training. After this training, the average number of errors made by experienced users shall not exceed two per day.

21 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 21 Requirements measures

22 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 22 Requirements interaction l Conflicts between different non-functional requirements are common in complex systems l Spacecraft system To minimise weight, the number of separate chips in the system should be minimised To minimise power consumption, lower power chips should be used However, using low power chips may mean that more chips have to be used. Which is the most critical requirement?

23 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 23 Domain requirements l Derived from the application domain and describe system characterisics and features that reflect the domain l May be new functional requirements, constraints on existing requirements or define specific computations l If domain requirements are not satisfied, the system may be unworkable

24 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 24 Library system domain requirements l There shall be a standard user interface to all databases which shall be based on the Z39.50 standard. l Because of copyright restrictions, some documents must be deleted immediately on arrival. Depending on the user’s requirements, these documents will either be printed locally on the system server for manually forwarding to the user or routed to a network printer.

25 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 25 Train protection system l The deceleration of the train shall be computed as: D train = D control + D gradient where D gradient is 9.81ms 2 * compensated gradient/alpha and where the values of 9.81ms 2 /alpha are known for different types of train.

26 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 26 Domain requirements problems l Understandability Requirements are expressed in the language of the application domain This is often not understood by software engineers developing the system l Implicitness Domain specialists understand the area so well that they do not think of making the domain requirements explicit

27 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 27 User requirements l Mendeskripsikan functional dan non-functional requirements sehingga dapat dipahami oleh pengguna sistem yang tidak memiliki pengetahuan teknis lebih detail l User requirements are defined using natural language, tables and diagrams

28 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 28 Problems with natural language l Lack of clarity Precision is difficult without making the document difficult to read l Requirements confusion Functional and non-functional requirements tend to be mixed-up l Requirements amalgamation Several different requirements may be expressed together

29 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 29 Database requirement 4.A.5 The database shall support the generation and control of configuration objects; that is, objects which are themselves groupings of other objects in the database. The configuration control facilities shall allow access to the objects in a version group by the use of an incomplete name.

30 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 30 Editor grid requirement 2.6 Grid facilities To assist in the positioning of entities on a diagram, the user may turn on a grid in either centimetres or inches, via an option on the control panel. Initially, the grid is off. The grid may be turned on and off at any time during an editing session and can be toggled between inches and centimetres at any time. A grid option will be provided on the reduce-to-fit view but the number of grid lines shown will be reduced to avoid filling the smaller diagram with grid lines.

31 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 31 Requirement problems l Database requirements includes both conceptual and detailed information Describes the concept of configuration control facilities Includes the detail that objects may be accessed using an incomplete name l Grid requirement mixes three different kinds of requirement Conceptual functional requirement (the need for a grid) Non-functional requirement (grid units) Non-functional UI requirement (grid switching)

32 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 32 Structured presentation

33 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 33 Detailed user requirement

34 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 34 Guidelines for writing requirements l Tentukan format standar dan gunakanlah dalam pembuatan semua dokumen requirements l Gunakan bahasa yang konsisten. l Gunakan text highlighting untuk mengidentifikasi bagian2 kunci pada requirement l Hindari menggunakan jargon komputer

35 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 35 System requirements l Spesifikasi lebih rinci dari user requirements l Menjadi basis bagi proses perancangan sistem l Dapat juga digunakan sebagai bagian dari kontrak sistem l System requirements dapat diekspresikan melalaui sistem model

36 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 36 Requirements and design l Secara prinsip, requirements akan menyebutkan apa yang harus dikerjakan oleh sistem dan design akan mendeskripsikan bagaiamana hal itu dikerjakan l Secara praktis, requirements dan design tidak terpisahkan A system architecture may be designed to structure the requirements The system may inter-operate with other systems that generate design requirements The use of a specific design may be a domain requirement

37 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 37 Problems with NL specification l Ambiguity The readers and writers of the requirement must interpret the same words in the same way. NL is naturally ambiguous so this is very difficult l Over-flexibility The same thing may be said in a number of different ways in the specification l Lack of modularisation NL structures are inadequate to structure system requirements

38 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 38 Alternatives to NL specification

39 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 39 Structured language specifications l A limited form of natural language may be used to express requirements l This removes some of the problems resulting from ambiguity and flexibility and imposes a degree of uniformity on a specification l Often bast supported using a forms-based approach

40 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 40 Form-based specifications l Definition of the function or entity l Description of inputs and where they come from l Description of outputs and where they go to l Indication of other entities required l Pre and post conditions (if appropriate) l The side effects (if any)

41 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 41 Form-based node specification

42 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 42 PDL-based requirements definition l Requirements may be defined operationally using a language like a programming language but with more flexibility of expression l Most appropriate in two situations Where an operation is specified as a sequence of actions and the order is important When hardware and software interfaces have to be specified l Disadvantages are The PDL may not be sufficiently expressive to define domain concepts The specification will be taken as a design rather than a specification

43 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 43 Part of an ATM specification

44 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 44 PDL disadvantages l PDL may not be sufficiently expressive to express the system functionality in an understandable way l Notation is only understandable to people with programming language knowledge l The requirement may be taken as a design specification rather than a model to help understand the system

45 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 45 Interface specification l Most systems must operate with other systems and the operating interfaces must be specified as part of the requirements l Three types of interface may have to be defined Procedural interfaces Data structures that are exchanged Data representations l Formal notations are an effective technique for interface specification

46 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 46 PDL interface description

47 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 47 The requirements document l Document requirements adalah pernyataan resmi mengenai apa yang dibutuhkan oleh pengembang sistem l Harus menyertakan definisi dan spesifikasi requirements l Dokumen ini BUKAN lah dokumen desain. Semaksimal mungkin paparkan APA yang harusnya dilakukan oleh sistem bukannya BAGAIMANA sistem akan mengerjakan hal tersebut

48 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 48 Requirements document requirements l Specify external system behaviour l Specify implementation constraints l Easy to change l Serve as reference tool for maintenance l Record forethought about the life cycle of the system i.e. predict changes l Characterise responses to unexpected events

49 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 49 IEEE requirements standard l Introduction l General description l Specific requirements l Appendices l Index l This is a generic structure that must be instantiated for specific systems

50 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 50 Requirements document structure l Introduction l Glossary l User requirements definition l System architecture l System requirements specification l System models l System evolution l Appendices l Index

51 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 51 Key points l Requirements berisi tentang apa yang dikerjakan sistem dan mendefiniskan batasan operasi dan implementasinya l Functional requirements merupakan produk/layanan yang disediakan oleh sistem l Non-functional requirements membatasi sistem yang sedang dikembangkan dan proses pengembangannya l User requirements adalah pernyataan umum tentang apa yang akan dikerjakan sistem

52 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 52 Key points l User requirements ditulis dalam bahasa natural, tabel dan diagram l System requirements dimaksudkan untuk mengkomunikasikan fungsi-fungsi yang disediakan oleh sistem l System requirements dapat ditulis dalam bahasa natural terstruktur, PDL atau dalam bahasa formal l Software requirements document adalah pernyataan kesepakatan tentang kebutuhan sistem