AspectOriented Requirements Engineering Awais Rashid Computing Department A

Aspect-Oriented Requirements Engineering Awais Rashid Computing Department © A. Rashid (2009)

Acknowledgements • I have worked with a number of people over the years on the topic of these lectures. They have all contributed to this work and a number of the slides. A special acknowledgement is due to the following persons: – Americo Sampaio, Ruzanna Chitchyan, Vander Alves, Paul Rayson, Alessandro Garcia, Nathan Weston and Peter Sawyer (Lancaster University, UK) – Ana Moreira and Joao Araujo (New University of Lisbon, Portugal) – Elisa Baniassad (Chinese University of Hong Kong, China) – Shmuel Katz (Technion-Israel Institute of Technology, Israel) – Monica Pinto and Lidia Fuentes (University of Malaga, Spain) Computing Department

Identifying Concerns in Requirements Computing Department

10. And a river went out of Eden to water the garden; and from thence it was parted, and became into four heads. 11. The name of the first is Pison: that is it which compasseth the whole land of Havilah, where there is gold; 12. And the gold of that land is good: there is bdellium and the onyx stone. 13. And the name of the second river is Gihon: the same is it that compasseth the whole land of Ethiopia. 14. And the name of the third river is Hiddekel: that is it which goeth toward the east of Assyria. And the fourth river is Euphrates. Computing Department Genesis 2: 10 -14

Where was the Garden of Eden? • • In Taurus Mountains in Anatolia, Turkey? Near Tabriz in North West Iran? Ethiopia? Java? Seychelles? Jackson County, Missouri? Bristol, Florida? … Computing Department

What is a Concern? Computing Department

Dijkstra’s View “It is what I sometimes have called "the separation of concerns", which, even if not perfectly possible, is yet the only available technique for effective ordering of one's thoughts, that I know of. This is what I mean by "focussing one's attention upon some aspect": it does not mean ignoring the other aspects, it is just doing justice to the fact that from this aspect’s point of view, the other is irrelevant. It is being one- and multiple-track minded simultaneously. E. W. Dijkstra, EWD 447, 1974 Computing Department

Parnas’ View “Every module in the … decomposition is characterized by its knowledge of a design decision which it hides from all others. Its interface or definition was chosen to reveal as little as possible about its inner workings. ” D. L. Parnas, CACM 15(12), 1972 Computing Department

Not One and the Same Thing • Separation of concerns is … … a principle to order one’s thoughts. Does not say what is a concern. • Modularity and information hidhing is … … about abstraction. Still need to find the suitable abstractions. Computing Department

A Concern is … “A concern is an interest which pertains to the system’s development, its operation or any other matters that are critical or otherwise important to one or more stakeholders. ” AOSD Ontology from AOSD-Europe Available from: http: //www. aosd-europe. net Computing Department

When do Concerns Manifest? Stakeholders Computing Department Designers/Developers

Expectation vs. Delivery Computing Department

Computing Department

Computing Department

“When a wise man, established well in virtue, Develops consciousness and understanding, Then as a bhikku ardent and sagacious, He succeeds in disentangling this tangle. ” Buddhaghosha (Visuddhimagga) Computing Department

Concerns in Requirements • Concerns first manifest themselves in requirements – Reflect stakeholders’ real concerns • Separation of concerns should begin with stakeholders’ concerns • But too many, often conflicting and overlapping, perspectives on the system Computing Department

Repeating Patterns of Concerns • Mostly same concerns appear in different concrete forms time and again in systems • Non-functional ones: – Security, Distribution, Persistence, Real-time, … • Functional ones: – Billing, Registration, Ordering, Booking, Business Rules, … Computing Department

Identifying Concerns Meta Concern Space Requirements Computing Department System Space

Use Case based Requirements Engineering • In a toll gate system, we must ensure that the vehicle gizmo is read between the moment the vehicle is detected by the system (when it is within ten meters of the toll gate) and enters the toll gate • Several use cases: read gizmo, enter motorway, exit motorway. Read gizmo Vehicle-gizmo Computing Department Enter motorway Exit motorway

Use Case based Requirements Engineering • A Shuttle Transport System Accountancy Monitor Accountancy Bid for Contract Computing Department Repair Shop

Is a Use Case a Concern? • A step-by-step usage path through a system – Such a path may run through multiple concerns • Use cases may overlap • No means to capture non-functional concerns Computing Department

Viewpoint-oriented Requirements Engineering • In a toll gate system, we must ensure that the vehicle gizmo is read between the moment the vehicle is detected by the system (when it is within ten meters of the toll gate) and enters the toll gate • Involves several user and system viewpoints: gizmo, vehicle, toll gate. Name Toll gate Focus … Concerns response time, securiy … Sources Name Vehicle Requirements. Focus … Concerns response time History … Name Gizmo Sources Focus … Requirements Concerns response time History … Computing Department Sources Requirements History

Is a Viewpoint a Concern? • A viewpoint represents the perspective of a stakeholder (user or system) on the system under development • Viewpoints naturally overlap • A viewpoint carries a slice of each concern relevant to the particular stakeholder – Not all concerns are relevant or as important for all stakeholders • Mostly focusing on functional concerns Computing Department

Goal-Oriented Requirements Engineering • In a toll gate system, we must ensure that the vehicle gizmo is read between the moment the vehicle is detected by the system (when it is within ten meters of the toll gate) and enters the toll gate • Distinguish between goal and soft goal Gizmo Vehicle Response Time Plate. Nr Gizmo is-part-of Detect. Vehicle Read. Gizmo Tollgate Computing Department is-part-of Response Time

Is a Goal a Concern? • Typically focused on broadly-scoped nonfunctional properties – Which are non-functional concerns • Catalogues of non-functional concerns Computing Department

The Problem of Crosscutting Concerns • The dominant decomposition – Slice requirements on the lines of viewpoints, use cases and goals • A number of concerns do not naturally fit these dominant decomposition boundaries Computing Department

Scattering and Tangling • Scattering – The specification of one property is not encapsulated in a single requirements unit, e. g. , a viewpoint, a use case. • Tangling – Each requirements unit contains descriptions of several properties or different functionalities Computing Department

Aspect-Oriented Requirements Engineering • Improved support for separation of crosscutting functional and non-functional properties during requirements engineering Improved understanding of the Identify the mapping and influence of requirements-level problem and ability to reason aspects on artefacts at later development stages about it – Establish critical trade-offs even before the architecture is – A better means to identify and manage conflicts arising due to tangled representations • derived • Trace aspectual requirements and their trade-offs to architecture and subsequently all the way to implementation Computing Department

AORE in the Broader RE Context Computing Department

Managing Crosscutting Concerns in Requirements • To find crosscutting in requirements, look for behavioural terms or concepts that are mentioned in more than one location • 1. Pay interest of a certain percent on each account making sure that the transaction is fully completed an audit history is kept. • 2. Allow customers to withdraw from their accounts, making sure that the transaction is fully completed an audit history is kept. Computing Department

Managing Crosscutting Concerns in Requirements • Separate each of those concepts into a section of their own 1. Pay interest of a certain percent on each account 2. Allow customers to withdraw from their accounts Computing Department 3. To fully complete a transaction. . . 4. To maintain an audit history. . .

Managing Crosscutting Concerns in Requirements • Composition specifies the crosscutting relationship, showing how crosscutting concerns affect base concerns 1. Pay interest of a certain percent on each account 2. Allow customers to withdraw from their accounts Fully complete pay interest and withdraw 3. To fully complete a transaction. . . Audit pay interest and withdraw 4. To maintain an audit history. . . Computing Department

Tyranny of Dominant Decomposition … again • Aspects capture crosscutting concerns • Analysed with reference to a base decomposition • What about concerns that do not fit the aspect boundaries? • Can we really capture all concerns effectively using such a base-aspect dichotomy? Computing Department

What Does the Tyranny mean in RE Terms? Broadly-scoped requirements, e. g. , goals, aspects, etc. Analysis conducted using Base decomposition: Functional Requirements (Viewpoints, use cases, etc. ) Main drivers for architectural quality analyses But why not these? Computing Department

Multi-Dimensional Nature of Concerns Computing Department

Concern Identification: The Scale of the Problem Computing Department

Concern Identification: A Solution? Computing Department

ts en m e r i u Req Computing Department

Requirements Sources • Requirements documents tend to be unstructured • Requirements can take a variety of forms – – – Natural Language Interviews Sketches Standardisation documents Organisational procedures ……… Computing Department

Concern Identification Challenges • Time consuming and error prone activities – Requirements elicitation and analysis • How to identify the concerns (or aspects, base abstractions, etc. )? • How the concepts are related? • How to structure them into a model? • Why? – Replication of requirements (crosscutting) and unrelated responsibilities (tangling) are difficult to find and separate – Documents can be of varied structure and nature (e. g. , user manuals, legacy specifications, e-mails, etc. ) – Size matters (e. g. , 5, 000 words document takes 20 minutes just to read) • Therefore – Tool support is vital for identifying concerns and structuring them into a suitable model for requirements analysis Computing Department

Thinking Multi-Disciplinary • Software is no longer an isolated entity • Part of a larger socio-technical system • Ethnography – To understand the processes by which concerns are identified and structured • Natural Language Analysis – To understand how concerns are expressed in natural language descriptions Computing Department

The EA-Miner Tool • Provides automation support for concern identification Uses Natural Language Processing (NLP) to reason about the properties and semantics of requirements expressed in natural language Can identify concerns in both asymmetric AORE models (e. g. , viewpoint-based) or multidimensional models Reduce the complexity (effort) of concern identification • • • – Not aimed at automating 100% of the tasks Computing Department

How EA-Miner Works? …All potential users of the system must first enroll with the system; once enrolled they have to log on to the system for each session. … (Requirement Document) WMATRIX NLP Processor EA-Miner <s> <w pos="DB" svo="" lemma="all" sem="N 5. 1+">All</w> • Identification of Concepts (e. g. , <w pos="JJ" svo="" lemma="potential" sem="DMOD"> viewpoints, early aspects, relationships) potential</w> • Filtering of candidates <w pos="NN 2" svo=“s" lemma="user" • Generation of concern model sem="A 1. 5. 1/S 2 mf">users</w> Computing Department </s> Plural noun

EA-Miner high level architecture View Generator Eclipse GUI Viewpoint View WMATRIX Controller Other Model View Specification Generator Viewpoint RDL in XML In Word File file Requirements to internal model parser Viewpoint Other Model parser Computing Department Internal model Viewpoint Other

Viewpoint-based AORE • Viewpoint groups requirements from the perspective of a stakeholder or other system (e. g. , Driver, ATM, Toll Gate on a toll System) • Viewpoints are base elements • Aspects are broadly scoped requirements that crosscut the viewpoints (e. g. , security, real-time) Computing Department

How EA-Miner Identifies Viewpoints and Aspects? • Based on Heuristics and NLP properties – For the Viewpoint-based AORE model, EA-miner identifies: • Viewpoints (based on POS tag): Nouns are the Viewpoint candidates • Non-functional Aspects: (Based on lexicon of NFRs and semantic tags): candidates are words found in the lexicon whose semantic tag is of interest • Functional Aspects: candidates are action verbs who are referenced in the requirements of several viewpoints. Computing Department

The NFRs lexicon • Used for the identification of non-functional aspects • Semantic tags are important for analysing the context – Performance: • Meaning 1: How well a football player performed • Meaning 2: A distributed system property • The lexicon was initially built re-using existing knowledge (NFR catalogues, domain experts) – Lexicon entries: <word content="authorise" sem="S 7. 4+" nfr="security"> </word> <word content=“performance" sem=“K 4" nfr=“performance"> </word> – Tool will suggest automatic updates in the future WMATRIX SEM class that groups words related to permission Computing Department

Requirements Description Language (RDL) • A multi-dimensional model – no base-aspect distinction • Makes natural language requirement semantics more explicit and bases composition on these semantics. • How? – Use grammatical information – Use semantic grouping from linguistics – Use natural language processing to help automation Computing Department

How EA-Miner Identifies Concerns for an RDL-based Analysis? • Based on Heuristics and NLP properties • NOUN-Based concerns (based on POS tag): Represent general entities and actors of the system. • Functional-based Concerns (Based on POS tag): Represent functionalities, operations. • NFR-based Concerns (Based on lexicon of NFRs and semantic tags): Represent broadly-scoped NFRs of the system. Computing Department

Computing Department

How Do We Know it Works? • 1 st Case Study: Comparison of 3 different systems between manual versus EA-Miner based approach – Research question: How well does EA-Miner perform when compared with a manual approach – Comparison Dimensions: Effort (Time Spent) and Quality of output: based on the judgment of a third senior engineer – Findings: • Improvements for the tool were found • Tool can provide valuable information and save time Computing Department

Comparative Results Computing Department

Comparative Results Computing Department

In an industrial Setting • 2 nd Case Study: INDUSTRIAL (Siemens) Case Study: toll system – Research question: How well does EA-Miner perform when used in a real industrial case study? – Findings: • The tool can help to spot important concerns missed by the developers as well as the requirements describing them in the source documentation Computing Department

Summary • Concerns first manifest themselves in requirements – This is where we must start to treat them • Concern identification is a non-trivial task – Requires us to go beyond our traditional software engineering boundaries • Tool support is essential to aid the requirements engineers in building concern models Computing Department

Selected Further Reading: Aspect. Oriented Requirements Engineering • Early Aspects Portal: http: //www. early-aspects. net. • Report synthesising state-of-the-art in aspect-oriented requirements engineering, architecture and design, Chitchyan et al. , Available from: http: //www. aosd-europe. net. • Modularisation and Composition of Aspectual Requirements, Rashid, Araujo, Moreira, Proc. AOSD Conference 2003, ACM. • Discovering Early Aspects, Baniassad, Clements, Araujo, Moreira, Rashid, Tekinerdogan, IEEE Software 23(1), Jan/Feb 2006. • Aspect-Oriented Requirements Engineering: an Introduction, Rashid, International Conference on Requirements Engineering (RE), 2008, IEEE CS. Computing Department

Selected Further Reading: Multi. Dimensional Models • N Degrees of Separation: Multi-Dimensional Separation of Concerns, Tarr, Ossher, Harrison, Sutton, Proc. International Conference on Software Engineering 1999, ACM. • Multi-dimensional Separation of Concerns in Requirements Engineering, Moreira, Rashid, Araujo, Proc. Requirements Engineering Conf. , 2005, IEEE CS Press. Computing Department

Selected Further Reading: EAMiner • Towards Automation in Aspect-Oriented Requirements Engineering, Sampaio, Rashid, Chitchyan, Rayson, To Appear in Transactions on Aspect-Oriented Software Development Special Issue on Early Aspects. • A Comparative Study of Aspect-Oriented Requirements Engineering Approaches, Sampaio, Greenwood, Garcia, Rashid, International Conference on Empirical Software Engineering and Metrics, 2007. IEEE CS • EA-Miner: A Tool for Automating Aspect-Oriented Requirements Identification, Sampaio, Chitchyan, Rashid, Rayson, Proc. International Conference on Automated Software Engineering 2005, ACM. Computing Department

Download and Play with EAMiner: http: //www. aosd-europe. net/deliverables/D 73 EAMiner. Distribution. zip • Includes: – – Installation Guide User manual Sample files Eclipse plug-in (. JAR) • WMatrix is accessible at: http: //www. comp. lancs. ac. uk/ucrel/wmatrix/ Computing Department

Concern Dependencies and Interactions Computing Department

“The first step towards the management of disease was replacement of demon theories and humours theories by the germ theory. That very step, the beginning of hope, in itself dashed all hopes of magical solutions. It told workers that progress would be made stepwise, at great effort, and that a persistent, unremitting care would have to be paid to a discipline of cleanliness. So it is with software engineering today. ” Fred Brookes, No Silver Bullet Computing Department

Why do We Wish to Separate Concerns? • Modular Reasoning – Keep concerns separated regardless of how they affect or influence various other concerns in the system, so that we can reason about each concern in isolation • Compositional Reasoning – Understand the dependencies and interactions amongst concerns to reason about the global or emergent properties of the system Computing Department

Two Types of Dependencies • At the requirements-level – How concerns influence or affect each other? – Which concerns reinforce each other and which ones conflict? – What are the trade-offs amongst concerns? • Beyond requirements analysis – How do concerns refine and map to architecture, design and implementation? – How changes in requirements affect the solutions we devise? – Does the resultant design and implementation meet stakeholders’ concerns? Computing Department

Requirements Dependencies and Interactions Computing Department

Alice through the Looking Glass Security Concern Computing Department Other Concerns

Trade-off Analysis • Basic questions – Are the solutions that are being suggested as good as possible? – How much must I give up to get a little more of what I want most? • How can we define a good / better outcome? – Reduced time of response – Improved security access – Increase number of clients being served simultaneously Computing Department

Decision Support • Finding the combination that better satisfies the stakeholder goals • What can actually be done given reality and resource constraints? – Use sophisticated techniques such as MCDM, fuzzy logic, etc. – Use some simple way to achieve a ranking between conflicting concerns (with the stakeholders help) Computing Department

Externalised Dependency Discovery • Discovering dependencies during the software development process – – – During release planning Change management Reuse Use cases … Computing Department

Discovering Intentional Dependencies • Study the semantics of requirements – Look at how and what stakeholders expressed – Inherently intentional dependencies • May not be obvious – Concerns may interact in subtle ways • A requirement may indirectly utilise data modified by another requirement • Improved connectivity would improve mobility Computing Department

Back to Multi-Disciplinarity • Linguistic models – Links between meaning of words and their grammatical representation • Example: – Archaic English verb gally – “Sailors gallied the whales” – “Whales gally easily” Computing Department to see to frighten

Grammatical Semantics to Understand Dependencies Concern Security R 1: Users must enrol with the system Subject Degree Relationship Computing Department Object

Subject-Object Dependencies • Direct dependencies – Understand links between requirements – An object in one requirement may form the subject of another requirement • Indirect dependencies – Discover data- and control-flow dependencies early on Computing Department

Dependencies through Synonyms • Users can be referred to in many ways in other requirements – – Customers Sellers Buyers … Computing Department

Dependencies and lemmatisation • Different terms may be variants of the same base form – enrols, enrolling and enrolment can be reduced to enrol • Simple syntactic or lexical match cannot reveal this dependency Computing Department

Semantic Dependencies • Different concerns may belong to the same semantic category – Authorisation, access control, etc. can be grouped into the same semantic category of Security. – May have reinforcement, dependent inclusion or mutual exclusion semantics • Or vice versa – May not belong to the same semantic category – Performance of the system vs. performance of the actor Computing Department

Relationship Semantics • Verbs express relationships between subjects and objects • Hence most fundamental to discovering dependencies • Dixon’s classification of verbs – Varying grammatical behaviour of verbs is due to differences in their meaning Computing Department

Dixon’s Verb Classification Computing Department

Patterns of Participating Roles • Giving type verbs require Donor, Gift and Recipient roles – Alan gave the keys to Peter. Donor Gift Recipient • Attention verbs require Perceiver and Impression roles – The instructor witnessed the accident. Perceiver Computing Department Impression

Condensing the Verb Categories • Positive and Negative sense of each verb category – Use: Utilise vs. Waste – Change: Increase vs. Decrease • Some categories are too fine-grained – Touch and Hit only differ in the intensity of the contact action – Look and Watch only differ in the duration of observation • Some categories could be amalgamated – Giving and Taking are opposites Computing Department

Condensing the Verb Categories Computing Department

Condensed Verb Categorisation Computing Department

How was it Condensed? • Some major groups remain – Affect, Move, Rest • Others amalgamated or repositioned – Attention and Thinking into Mental Action – Speaking and Show into Communicate • General Actions as a convenience group for action verbs • Still retain the patterns of participating roles Computing Department

Reasoning about Influences Computing Department

Relative Degrees of Importance and Influence Computing Department

Dependencies Across the Lifecycle Computing Department

“Enter and ask”. An inscription in the Alhambra in Granada. Computing Department

Issues on Mapping and Traceability • Is a requirements concern always a design and implementation module? • How do requirements concerns map onto later development stages? • How can we ensure forward and backward traceability between requirements concerns and corresponding architecture, design and implementation? • How do we know that the requirements concern tradeoffs are preserved and respected by the design and implementation? Computing Department

Mapping Compatibility Concern to Architecture Computing Department

How do Requirements Concerns Map onto Later Development Stages? • A concern in requirements may be resolved as non-software solution (e. g. for some business hiring a security guard to satisfy a Security concern → no mapping to software architecture) • Architectural Decision (e. g. , the architectural topology for Compatibility concern) • Architectural Module or an element of a module which has localised influence in architecture (e. g. , a method checking correctness or some processing within a component) • Aspectual Architectural Modules which influence a number of other architectural components (e. g. , a module providing encryption and decryption functionality) Computing Department

Concern Traceability • As always need Tool Support for Traceability, but – Dedicated modules for concerns at various levels help with direct mapping where appropriate – Composition specifications at various levels help in tracing influences: • Examples of composition specifications in Architecture are bindings in ADL supported in connectors or dedicated composition languages as part of traceability templates – Correspondence between meta-models of requirements and architecture (etc. ) elements helps with mapping and traceability guidelines. • Mapping patterns of concern compositions in requirements to patterns of component or aspect compositions in architecture, design and implementation Computing Department

Concerns Driving Architectural Choices Concerns Architecture Choices Response Time … Availability … . . Security Computing Department . . …

Where Does the Final Architecture Reside? Computing Department Architecture Availability Performance Security Multi-access

Are Trade-offs Preserved and Respected? • Need to connect concerns to their concrete realisations in design and implementation – Need to know that trade-offs established at requirements level are preserved in the implementation • Needs precise semantics for requirements • Proof obligations may be used for: – Formal verification of the resultant system (e. g. , via model checking) – Deriving test cases Computing Department

Concern Proof Obligations • Temporal logic formulas about concern • Group individual formulas to those treating each concern • Must treat potential conflicts among concerns (as identified in requirements) Computing Department

Temporal Logic Formulas • • • Gp: from now on, p is true Fp: eventually, p will be true p. Uq: p is true until q becomes true Can be input formal methods tools G((veh-ent-sys ((Fveh-ent-toll)/ ((¬veh-ent-toll)Uread-gizmo)))/(readgizmo-effects) / (time(veh-ent-toll) – time(veh-ent-sys) < N)) Computing Department

Conflict Analysis • Multiple concerns with contradictory requirements – Availability ( backup system) vs Response Time • Often requires preferring one over the other or weakening for real conflicts • Solution: weakened properties for conflict resolution – Weak Resp. Time: … time(E 2) – time (E 1)<N+Extra Computing Department

The Resulting Proof Obligations • Collection of temporal formulas from the requirements with predicates instantiated • Possibly weakened versions for conflicts • Assertion of non-interference among concerns • Assertion that desirable properties of the system are still true as new concerns are augmented during incremental development Computing Department

Summary • Dependencies and interactions are not a problem – They are inherent and essential to the systems we are trying to analyse and design – Understanding them is essential for effective compositional reasoning • Semantics of the natural language capture such dependencies and interactions – Can be used to expose and study them • Clearer mapping of concerns to architecture and beyond • Early trade-off analysis and resolution • Improved traceability of stakeholders’ concerns to the solution and its implementation Computing Department

Selected Further Reading: Verb Classification • A Semantic Approach to English Grammar, 2 ed. , Dixon, Oxford University Press, 2005. • English Verb Classes and Alternations: A Preliminary Investigation, Levin, University of Chicago Press, 1993. Computing Department

Selected Further Reading: Concern Dependency Semantics • Semantics-based Composition for Aspect. Oriented Requirements Engineering, Chitchyan, Rashid, Rayson, Waters, International Conference on Aspect-Oriented Software Development (AOSD), 2007, ACM. • Tracing Requirements Interdependency Semantics, Chitchyan, Rashid, Early Aspects 2006: Traceability of Aspects in the Early Life Cycle Workshop at AOSD 2006. Computing Department

Selected Further Reading: Concern Mappings • COMPASS: Composition-Centric Mapping of Aspectual Requirements to Architecture, Chitchyan, Pinto, Rashid, Fuentes, Transactions on Aspect-Oriented Software Development: Special Issue on Early Aspects, Accepted to Appear. • From Aspectual Requirements to Proof Obligations for Aspect-Oriented Systems, Katz, Rashid. International Conference on Requirements Engineering (RE), 2004, IEEE Computer Society. Computing Department

Semantics-based Composition of Concerns Computing Department

“Oh! thou great Lycurgus, that com’st to my beautiful dwelling, Dear to Jove, and to all who sit in the halls of Olympus, Whether to hail thee a god I know not, or only a mortal, But my hope is strong that a god thou wilt prove, Lycurgus. ” Pythoness of Delphi to Lycurgus of Sparta (Herodotus: The Histories) Computing Department

Recap • What have we Looked at so Far? – Concerns in requirements represent real concerns of the stakeholders – Natural language semantics can give clues about: • Nature of concerns • Their relationships and interdependencies • Next: – We look at how to exploit these semantics for composition and analysis – Using the Requirements Description Language (RDL) Computing Department

How does it all Fit Together? Concern Identification Concern Elicitation Concern Representation Requirement Refinement Requirement Mapping Computing Department RDL Link RE & Architecture EA-Miner Requirement Composition Trade-Off Resolution

Problems of Syntactic Matching • Composition specified in terms of structure (so must map content to structure); Concern Bidding Rn: Buyers are bidding for goods. Concern Security R 1: Users must enrol with the system Composition Secure Bidding concern= Security id= R 1 concern= Bidding id= Rn … Computing Department

Problems of Syntactic Matching • Infer the semantics of the relationships back from structure to reason Composition Secure Bidding concern= Security id= R 1 concern= Bidding id= Rn … Computing Department

Problems of Syntactic Matching • Must define each joinpoint/composition point manually: – give id/name to each relevant point – must know ahead these points, or – constantly refactor • Fragile compositions: e. g. , add new requirement to violate all id references. Concern Security : A secure protocol must be used. RR 11: Users must enrol with the system; a secure protocol must be used. R : Users must enrol with the system. 2 Composition Secure Bidding concern= Security id= R 1 concern= Bidding id= R Computing Department n …

Syntactic Matching in AOSDbased Use Cases Computing Department

Syntactic Matching in Viewpoint-based AORE <Viewpoint name=“Customer”> <Requirement id=“ 1”>The customer selects the room type to view room facilities. </Requirement> <Requirement id=“ 2”> The customer makes a reservation for the chosen room type with the given room price. </Requirement> … </Viewpoint> (a) <aspect name=“Cache. Access”> <Requirement id=“ 1”>The system looks up cache when : <Requirement id=“ 1. 1”> room type data is accessed; </Requirement> <Requirement id=“ 1. 2”> room pricing data is accessed; </Requirement> </aspect> (b) <Composition> <Requirement aspect=“Cache. Access" id=“ 1. 1"> Computing Department <Constraint action=“provide" operator=“for"> <Requirement viewpoint=“Customer" id=“ 1" /> … (c)

Three key problems • Map developer’s intentionality onto a syntax governed structural model • Infer semantic influences and interferences from syntactic compositions • Composition fragility Computing Department

Semantics-based Composition with the RDL • Make natural language requirement semantics more explicit and base composition on these semantics. • How? – – Use grammatical information Use semantic grouping from linguistics Use natural language processing to help automation Basically what we have been talking about in the last lecture! Computing Department

Requirements Description Language Elements Requirement Subject Object Relationship Degree Computing Department Concern

RDL Concern Example Concern Security R 1: Users must enrol with the system Subject Degree Relationship Object <Concern name=“Security”> <Requirement id=“ 1”> <Subject> Users </Subject> <Degree type=“Modal” semantics=“Modal” level=“high”> must </Degree> <Relationship type=“Move” semantics=“Group”>enrol </Relationship> with the <Object> system </Object> </Requirement> Computing </Concern> Department

Requirements Description Language Composition Elements Advise Base Constraint Concern B Concern A Req. 1 Req. 2 Outcome Req. 1 Req. k Req. 2 Req. x Req. n Req. y Computing Department Req. z

Semantic Queries Query: Select the requirements where user enrols or a system is enrolled to. RDL Query all requirements where ( Subject=“users” and Relationship=“enrol” ) or ( Relationship=“enrol” ) Computing Department Object=“system” and Also used in Queries for matching: Synonyms: register, sign up, join… Lemmas: enrol, enrolled, enrolling. .

RDL Composition Example Composition: Apply the requirements where user enrols to a system before any buyer bids. <Composition name=“Secure. Bidding”> <Constraint operator=“apply”> subject= “user” and relationship= “enrol” and object=“system” </Constraint> <Base operator=“before”> subject=“buyer” and relationship=“bid” </Base> <Outcome operator=”satisfied”/> </Composition> Computing Department

Composition Sequencing Operators Computing Department

Verb Type-based Query Composition: Apply the requirements where user enrols to a system before all types of activities where goods are exchanged. <Composition name=“Comp. Access. Cache”> <Constraint operator=“apply”> subject= “user” and relationship= “enrol” and object=“system” </Constraint> <Base operator=“before”> relationship. semantics= “Transfer_Posession” object=“goods”</Base> </Concern> Computing Department

Degree Type Based Query Composition: Constraint requirement “Include requirements into 1 st release” should be applied for all requirements which have Modal verbs of high importance. <Composition name=“Comp. First. Relase”> <Constraint operator=“include”> “Include requirements into 1 st release” </Constraint> <Base operator=“if”> degree. semantics=“Modal” and degree. level=“high”</Base> </Concern> Computing Department

Automation Support: Wmatrix • Wmatrix Natural Language Processor – Semantic Category Annotation – Part of Speech (POS) Annotation – Using the POS tags form rules for Subject, Relationship, and Object identification (continuously improving) – Map RDL verb classes onto Wmatrix native classification (continuously improving) • Used as the backend of EA-Miner, which generates the annotated files for analysis tools Computing Department

Composition Challenges • Multidimensional modularity implies high complexity and low scalability • Reducing compositional combinations (and hence semantic graphs) – Critical for reasonable response to change / limited resources with larger specifications – Compositional intersection • i. e. , orphan semantic links are not included – Elimination of some potential combinations Computing Department

Trade-off Analysis using Compositional Intersection • Need to observe trade-offs with respect to some base! – Too many possible combinations when projecting every possible set of concerns on every other possible set • Let C 1, C 2, C 3, …, Cn be the concrete concerns in our requirements spec. • Let Sc 1, Sc 2, Sc 3, …, Scn be the sets of concerns that each of them cuts across • C 1 C 2 = Ca iff both C 1 and C 2 semantically influence/constrain the same or overlapping set of requirements in Ca Computing Department

Cumulative Effect of Concern Contributions val Mobi e i r t e labil lity R n o i i t t y Availability rma o U} {Co f I n , I b nt, N Mo , Information v a av} st, N {Cus u C { Retrieval t, Na v, M { N ob, I av} Mobility U } { C } ont, N. . . {Nav av} Computing Department . . . Avai

Architectural Choices Concerns Architecture Choices Inf. Ret. … Availability … . . Mobility Computing Department . . …

Where Does the Final Architecture Reside? Computing Department

How to Map to Architecture? Computing Department

SRO Mapping Computing Department

Summary • How RDL Addresses Problems of Syntactic Composition? – – Composition specified in terms of intentional semantics No need for manual joinpoint definition Clear semantics of concern relationships from compositions Composition fragility ameliorated: will either match or not depending on the semantics • Tool support from WMatrix and EA-Miner helps with identification, representation, composition and analysis of semantic dependencies • Map patterns of concern compositions in requirements to patterns of architecture composition Computing Department

Selected Further Reading: RDL • Semantics-based Composition for Aspect-Oriented Requirements Engineering, Chitchyan, Rashid, Rayson, Waters, International Conference on Aspect-Oriented Software Development (AOSD), 2007, ACM. • A Formal Approach to Semantic Composition of Aspect. Oriented Requirements, Weston, Chitchyan, Rashid, International Conference on Requirements Engineering (RE), 2008, IEEE CS. Computing Department

Selected Further Reading: Mapping • COMPASS: Composition-Centric Mapping of Aspectual Requirements to Architecture, Chitchyan, Pinto, Rashid, Fuentes, Transactions on Aspect-Oriented Software Development: Special Issue on Early Aspects, Accepted to Appear. Computing Department

Further Information awais@comp. lancs. ac. uk http: //www. comp. lancs. ac. uk/computing/aose http: //www. aosd-europe. net Computing Department