Kon-41 4011 Modeling Requirements
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Systems Thinking and Systems Engineering
Systems Engineering: Requirements model
07 February 2013
François Christophe
Galina Medyna
Eric Coatanéa
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Objectives of the lecture
1. Know different types of representations for requirements
2. Understand the importance of modeling requirements
3. Apply techniques for refining requirements
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Definition of requirement structure
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Structure of requirement
1- Identified: Qualitatively defined, this is a need,
2- Specified: Quantitatively defined, this is a specified requirement,
3- Allocated: Assigned to a product, process, subsystem or a combination,
4- Covered: Satisfied by the element to which it has been allocated
A requirement is:
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Structure of requirement
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Structure of requirement
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Types of representations of requirements
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Representation types
• Document• Classification of requirements under categories• List of requirements• Tree of Requirements• Detailed requirements with performance values
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Requirements document
http://www.c-jump.com/CIS75/Week06/samples/requirements.html
http://www.swisseurobot.ch/images/2012/e2012_rules_en_final.pdf
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Classification of requirements
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Classification of requirements
User requirements
Technical requirements
Adapted from: Hull, E., Jackson, K., Dick, Jeremy., 2005, Requirement Engineering, 2nd ed., Springer, London.
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Classification of requirements• Business requirements:
– High level requirements related to company organisation
• User (stakeholder) requirements– Requirements related to user wishes or needs from a project
• Functional requirements– Functionalities required from a system derived from analysis of user
requirements
• Non-functional requirements– Requirements related to constraints such as cost, performance,
dimension, maintenance...
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List of requirements
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Tree of requirements
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Detailed requirements
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Detailed requirements
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Detailed requirements
• A detailed requirement should be quantitatively defined (specified)– Can be defined with its utility
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Detailed requirements:Trade-offs between requirements• Example:
– Power source should provide enough energy for playing 2 matches consecutively: (2*90s.)
BUT– Constraints for the robot dimensions
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Allocated requirements
• Requirements should be allocated to specific parts of the system
• Examples of allocation:
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Why is it important to model requirements?
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Model of requirements? Why?
• Siemens PLM requirements• Dassault RFLP• Providia• IBM Rational Doors
Why so many vendors give importance to requirement modeling?
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Because...
• Requirements descriptions are similar to a contract between customers and suppliers
• It is important to capture the interactions and possible contradictions between requirements (contradictions can lead to design constraints)
• It is important to keep track of initial objectives– Allocation and satisfaction mechanisms used for traceability
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Refinement techniques
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Functional or non-functional?
• Analysis of types of verbs and objects used in requirements sentences
• Helps classifying requirements into different categories
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Functional or non-functional?
A requirement is a sentence in natural language.
A function is always related to transitive and intransitive verbs.
Examples:
The seat must prevent injury (seat=subject, prevent= transitive verb, injury=object)
The airplane seat must float. (seat =subject, float =intransitive verb)
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Functional or non-functional?Third type of requirement sentences exist: sentences
where the verb is a linking verb
Example:
The seat must be easy to adjust.
(seat=subject, be=linking verb, easy to adjust=subject compliment)
In this type of sentence, the verb is not representing an action, this structure of sentence is representing
a non-functional requirement.
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Classifying rules from grammatical structures
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Tool example
• This tool defines specific grammatical structures for expressing requirements:
http://freespace.virgin.net/gbjedi/books/re/boilerplates/repository.htm
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Common keywords
• Finding common keywords in different requirements sentences
• Helps finding links/interactions/contradictions between 2 requirements from different categories
• Example: file:///C:/Users/Francois/Desktop/MadeByGraph/simAnalysis.htm
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Searching for required performance
From Qualitative to Quantitative requirements:• For requirements containing comparative or superlative
such as: easier, better, simpler, faster
• Ask about:– What does the comparative or superlative refer to?
– How to measure?
– Which unit?
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Searching for required performance
• Words like never, always, ever, everybody, nobody, all: – often generalize a fact
• Ask about:– Really always?– Really everybody?– Really never?
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Thank for your attention
Exercises:
- Analyse EU-robot rules document.
- Extract requirements related to the objectives of your own project