© Colin Potts C4-1 Information-oriented approaches Colin Potts Georgia Tech

© Colin Potts C4-2 Information modeling in the enterprise l Philosophy »Systems are what they are about, not what they do »Therefore, model the system’s subject matter –Process and computation is secondary »Information structure is more stable in the enterprise than functions & processes

© Colin Potts C4-3 Information modeling & requirements l Many organizations are developing enterprise data models / schemas »Requirements for new applications must be described in the terminology of the model Enterprise- wide model Applications

© Colin Potts C4-4 Entity-relationship (ER) modeling l Subject matter is described in terms of »Entities »Relationships »Attributes »Constraints l ER-modeling is not restricted to database design »Though most relevant for DB-intensive ISs Patron Book borrows Title Author copy of attribute relationship entity

© Colin Potts C4-5 Entities & relationships l Entities are things »but not necessarily tangible (books), also abstract concepts (title) l Relationships hold in states »System exists in discrete states »e.g. “Fred has borrowed War and Peace” patron book entity

© Colin Potts C4-6 Attributes & cardinality l Attributes are properties of entities »Though sometimes, an apparent attribute gets “promoted” to a relationship l Cardinality constraints say how many entities of each type can participate »Minimum and maximum at each end of relationship

© Colin Potts C4-7 Cardinality (cont.) l Min 0 »entity may enter into relationship l Min 1 »entity must enter into relationship l Max 1 »entity enters into relationship with at most one other entities l Max n »entity may enter into relationship with others entity 1 entity 2 relationship

© Colin Potts C4-8 Translating a model into English N MN MN MN M An M verbs Ns An M verbs an N An M may verb an N An M may verb Ns

© Colin Potts C4-9 Transactions & updates l Transactions are operations that affect the state of the model »e.g. use cases in a BPR model »effects may be –create –retrieve –update –delete of an entity, its attributes or relationships l “CRUD matrix”

© Colin Potts C4-10 Team exercise: Information modeling l As a class »Think about problem domain that underpins the example requirements »Identify candidate entities, attributes, relationships from domain l In teams of 2-3 »Sketch E-R model fragment l As a class »Discuss the insights so gained about the reqts.

© Colin Potts C4-11 Information modeling: how to find out more l There are many books on information modeling »but most are about DB design l Two good general introductions are »Shlaer & Mellor (Don’t be deceived by the “OO” title) »Barker: CASE Method

© Colin Potts C4-12 Object-oriented analysis: introduction l OOA evolved from Information Modeling »Very similar in outline l OOA is analysis and specification phase preceding OOD/OOP l Relevance to requirements »As with information modeling, derive requirements using terminology of stable object model

© Colin Potts C4-13 Objects and entities l OOA and information modeling have same basic concepts »Classes = Entity classes »Objects = Instances »Objects have operations »Objects have life cycles »Some classes specialize others from which they inherit attributes and operations Title author Loaner has copy (1,1) (1,n) Patron name borrows (0,1) (0,n) acqn# Book

© Colin Potts C4-14 Two families of OOA/OOD methods l OOA associations can be purely static relationships »cf. information modeling; conditions that hold l Or can be dynamic connections »cf. modules using other modules l Two families of methods »IM-based: ERA plus inheritance & ops. »Dynamic: Based on scenarios.

© Colin Potts C4-15 Objects and scenarios of use l OMT (Rumbaugh et al) »Heuristics for identifying classes »Dynamic model –Build scenarios describing how system will be used –Draw event traces for the scenarios showing objects interacting –Develop lifecycle models (state machines for classes Patron Book borrow return Patron shelved on loan borrow return

© Colin Potts C4-16 Objects and operations OMT object model »Operations are treated like a special type of attribute »Operations may be performed or suffered »Operations change the value of an attribute or relation –Here "borrowed" Similar treatment in other OOA methods acqn# Book Patron name borrow return borrowed (0,1) (0,n)

© Colin Potts C4-17 OOA: how to find out more l There are lots of methods and books about them l OOA as extended information modeling »Rumbaugh et al book l OOA as scenario-based analysis method »Jacobson book –Different from the BPR book

© Colin Potts C4-18 Conclusions: Information- oriented approaches l Goal »Understand requirements through constructing information model l Techniques »ER modeling & OOA l Evaluation »ER is mature, but unnecessarily restricted to DB design »OOA is new