Lezione 2 Lezione 2 Software requirements requirements Software - - PDF document
Corso di Laurea Magistrale Corso di Laurea Magistrale in in Ingegneria Informatica Ingegneria Informatica per la Gestione d azienda azienda per la Gestione d Gestione della Qualit-II parte Il progetto software: metodologie e
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a.a. a.a. 2010 2010-
2011
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– – The complete The complete description description of
the functions functions to to be be performed performed by by the software the software will will assist the assist the users users to to determine determine if if the the software software meets meets their their needs needs or
how the software the software must must be be modified modified to to meet meet their their needs needs. .
– – The The preparation preparation of
a document document forces forces the the customers customers to to consider consider rigorously rigorously all all of
the requirements requirements before before design design begins begins and and reduces reduces later later redesign redesign, , recoding recoding, and , and retesting retesting. . Careful Careful review review of
the specified specified requirements requirements can can reveal reveal
, misunderstandings misunderstandings, and , and inconsistencies inconsistencies early early in the in the development development cycle cycle when when these these problems problems are are easier easier to to correct correct. .
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– – The The description description of
the product product is is a a realistic realistic basis basis for for estimating estimating project project costs costs. .
– – Organizations Organizations can can develop develop their their validation validation plans plans much much more more productively productively , , as as a part a part of
the development development contract contract, the , the specification specification document document provides provides a a baseline baseline against against which which compliance compliance can can be be measured measured. .
– – A A good good specification specification document document makes makes it it easier easier to to transfer the transfer the software software product product to to new new users users or
new machines machines. .
– – The The document document may may need need to to be be altered altered, , but but it it does does provide provide a a foundation foundation for for continued continued production production evaluation evaluation. .
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The The basic basic issues issues that that the SRS the SRS writer writer(s) (s) shall shall address address are the are the following following: :
Functionality. .
– – What What is is the software the software supposed supposed to to do? do?
External interfaces interfaces. .
– – How How does does the software the software interact interact with with people, the system people, the system’ ’s hardware, s hardware,
hardware and other
software?
Performance.
– – What What is is the the speed speed, , availability availability, , response response time time, , recovery recovery time time of
various software software functions functions, etc.? , etc.?
Attributes. .
– – What What are the are the portability portability, , correctness correctness, , maintainability maintainability, security, etc. , security, etc. considerations considerations? ?
Design constraints constraints imposed imposed on
an implementation implementation. .
– – Are Are there there any any required required standards standards in in effect effect, , implementation implementation language language, , policies policies for for database database integrity integrity, , resource resource limits limits, , operating
environment environment(s) etc.? (s) etc.?
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– – Customers Customers usually usually do do not not understand understand the software design and the software design and development development process process well well enough enough to to write write a a usable usable SRS. SRS. – – Suppliers Suppliers usually usually do do not not understand understand the the customers customers problem problem and and field field of
endeavor well well enough enough to to specify specify requirements requirements for for a a satisfactory satisfactory system. system.
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The SRS may may need need to to evolve evolve as as the the development development of
the software product product progresses progresses. . It It may may be be impossible impossible to to specify specify some some details details at the at the time time the project the project is is initiated initiated; ; additional additional changes changes may may ensue ensue as as deficiencies deficiencies, and , and inaccuracies inaccuracies are are discovered discovered in the SRS. in the SRS.
Two major major considerations considerations in in this this process process are the are the following following: :
– – Requirements Requirements should should be be specified specified as as completely completely and and thoroughly thoroughly as as is is known known at the at the time time, , even even if if evolutionary evolutionary revisions revisions can can be be foreseen foreseen as as inevitable
. The fact fact that that they they are incomplete are incomplete should should be be noted noted. . – – A A formal formal change change process process should should be be initiated initiated to to identify identify, , control control, , track track, , and report and report projected projected changes changes. .
Approved changes changes in in requirements requirements should should be be incorporated incorporated in the in the SRS in SRS in such such a way a way as as to to
– – Provide Provide an an accurate and complete accurate and complete audit audit trail trail of
changes; ; – – Permit Permit the the review review of
current and and superseded superseded portions portions of
the SRS.
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Prototyping is is used used frequently frequently during during the the requirements requirements portion portion of
a project.
Many tools tools exist exist that that allow allow a a prototype prototype, , exhibiting exhibiting some some characteristics characteristics of
a system, to to be be created created very very quickly quickly and and easily easily. . Prototypes Prototypes are are useful useful for for the the following following reasons reasons: :
– – The The customer customer may may be be more more likely likely to to view view the the prototype prototype and and react react to to it it than than to to read read the SRS and the SRS and react react to to it it. . Thus Thus, the , the prototype prototype provides provides quick quick feedback. feedback. – – The The prototype prototype displays displays unanticipated unanticipated aspects aspects of
the systems systems behavior behavior. . Thus Thus, , it it produces produces not not only
answers but but also also new new questions questions. . This This helps helps reach reach closure closure on the SRS.
– – An SRS An SRS based based on a
prototype tends tends to to undergo undergo less less change change during during development development, , thus thus shortening shortening development development time time. .
A prototype prototype should should be be used used as as a way a way to to elicit elicit software software requirements
. Some characteristics characteristics can can be be extracted extracted directly directly from from the the prototype prototype, , while while other
requirements can can be be inferred inferred by by running running experiments experiments with with the the prototype prototype. .
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– – A A systematic systematic evaluation evaluation of
a software product product by by a team a team of
qualified qualified personnel personnel that that examines examines the the suitability suitability of
the software software product product for for its its intended intended use use and and identifies identifies discrepancies discrepancies from from specifications specifications. . Technical Technical reviews reviews may may also also provide provide recommendations recommendations of
alternatives and and examination examination of
various various alternatives alternatives. .
– – A A static static analysis analysis technique technique in in which which a designer or a designer or programmer programmer leads leads members members of
the development development team and team and other
interested parties parties through through a software a software product product, and the , and the participants participants ask ask questions questions and and make make comments comments about about possible possible errors errors and and other
problems problems. .
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anomaly
– – Any Any condition condition that that deviates deviates from from expectations expectations based based on
requirements specifications specifications, design , design documents documents, , user user documents documents, , standards standards, etc., or , etc., or from from someone someone’ ’s s perceptions perceptions or
experiences. . Anomalies Anomalies may may be be found found during during, , but but not not limited limited to to, the , the review review, test, , test, analysis analysis, compilation, or , compilation, or use use
software products products or
applicable documentation documentation. .
audit
– – An An independent independent examination examination of
software products products or
processes to to assess assess compliance compliance with with specifications specifications, , standards standards, , contractual contractual agreements agreements, or , or other
criteria. .
inspection
– – An An examination examination of
a software product product to to detect detect and and identify identify anomalies anomalies, , including including errors errors and and deviations deviations from from standards standards and and specifications specifications. . Inspections Inspections are are peer peer examinations examinations led led by by impartial impartial facilitators facilitators who who are are trained trained in in inspection inspection techniques techniques. . Determination Determination of
remedial remedial or investigative
action for for an an anomaly anomaly is is a a mandatory mandatory element element
a software inspection inspection, , although although the the solution solution should should not not be be determined determined in the in the inspection inspection meeting. meeting.
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A requirement requirement specifies specifies an an externally externally visible visible function function or
attribute
a system. A design describes describes a a particular particular subcomponent subcomponent of
a system and/or system and/or its its interfaces interfaces with with other
. The SRS writer writer(s) (s) should should clearly clearly distinguish distinguish between between identifying identifying required required design design constraints constraints and and projecting projecting a a specific specific design. Note
that every every requirement requirement in the SRS in the SRS limits limits design design alternatives alternatives. . This This does does not not mean mean, , though though, , that that every every requirement requirement is is design. design.
The SRS should should specify specify what what functions functions are are to to be be performed performed on
what what data data to to produce produce what what results results at at what what location location for for whom
. The SRS SRS should should focus on the focus on the services services to to be be performed
. The SRS should should not not normally normally specify specify design design items items such such as as the the following following: :
– – Partitioning Partitioning the software the software into into modules modules; ; – – Allocating Allocating functions functions to to the the modules modules; ; – – Describing Describing the flow the flow of
information or control control between between modules modules; ; – – Choosing Choosing data data structures structures. .
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– – certain certain functions functions are are kept kept in separate in separate modules modules; ; – – only
limited communication communication between between some some areas areas of
the program program are are permitted permitted. .
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The SRS should should address address the software the software product product, , not not the the process process of
producing producing the software the software product product. .
Project requirements requirements as as
– – Cost Cost – – Delivery Delivery schedules schedules – – Reporting Reporting procedures procedures; ; – – Software Software development development methods methods – – Quality Quality assurance assurance; ; – – Validation Validation and and verifcation verifcation criteria criteria – – Acceptance Acceptance procedures procedures. .
represent represent an an understanding understanding between between the the customer customer and the and the supplier supplier about about contractual contractual matters matters pertaining pertaining to to production production of
software and and thus thus should should not not be be included included in the SRS. in the SRS.
Project requirements requirements are are specified specified in in other
documents, , like like as as a a software software development development plan plan, a software , a software quality quality assurance assurance plan plan, or a , or a statement statement of
work.
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– – Provide Provide a complete a complete list list of
all documents documents referenced referenced elsewhere elsewhere in the SRS; in the SRS; – – Identify Identify each each document document by by title title, date, and , date, and publishing publishing
; – – Specify Specify the the sources sources from from which which the the references references can can be be
.
– – Describe Describe what what the the rest rest of
the SRS contains contains; ; – – Explain Explain how how the SRS the SRS is is organized
.
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globalità;
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