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## CS551 Modelling with Objects (Chap. 3 of UML)

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**CS551 Modelling with Objects(Chap. 3 of UML)**Yugi Lee STB #555 (816) 235-5932 yugi@cstp.umkc.edu www.cstp.umkc.edu/~yugi CS551 - Lecture 8**Object Modelling**• Static model: the state of an object at any given moment (object attributes, relationships, constraints between objects) • Dynamic model: the changes that happen to the state as event occur (actions affect objects, using the changes of objects and attributes in the object state) • Interactive model: interactions between objects (the responsibility for achieving goal is divided among collaborating objects) CS551 - Lecture 8**Modeling Objects: Definitions**• Object: anything that presents a definable encapsulated behavior to the world around it; e.g. individual programming-language objects, software components, programs, • Type: a collection of objects with similar behaviors, satisfying the specification of that type • Type model: Behaviors are specified in terms of attributes, a valid abstract model of many possible implementations. CS551 - Lecture 8**Static Model**• The state of an object at any given point in time: individual identity, characteristic behavior, and state (a combination of stored state and executable code) • a set of attributes: properties that define information on the state of the object at any point in time; e.g. a set of LineItems (quantity of a product), the orderTotal, and the Customer. • a set of static invariants: rules on what combinations of attribute values are valid for that object's state to be valid; e.g. "no two LineItems can be for the same Product", or "the orderTotal cannot be greater than the customer's credit limit". CS551 - Lecture 8**System of Interest**Model of object types for terms used to specify system operations Not a stored data model Interface Operations of System Type Model Sales System <<type>> currSale Product inventory * Sale Cust Object type and abstract attribute * * SaleItem quantity Payment Authorization CS551 - Lecture 8**Modeling State**• A snapshot shows a set of objects and their configuration at a point in time (the values of their attributes or links to other objects). • A filmstrip shows a sequence of snapshots evolving through the steps of a scenario. CS551 - Lecture 8**Modeling Object State**• Attributes: model and reality • Parameterized attribute • session-5.startDate.isLessThan (today) • session-5.startDate < today • Association: a pair of attributes that are inverses of each other, drawn as a line joining the two types on a type model. CS551 - Lecture 8**Modeling Object State: Invariants**• Collections • Set: a collection of objects without any duplicates; • Bag: a collection with duplicates of elements; • Seq: a sequence-a bag with an ordering of its elements. • Operators: • dot (“.”) operator for a collection evaluates an attribute on every element of the collection; e.g., clients.sessions = Set {s1, s5, s9} • The -> operator for a collection evaluates an attribute on the collection itself; e.g., client3.sessions -> count =3 CS551 - Lecture 8**Modeling Object State: Invariants**• forAll, exists //every one of laura’s session grades is better than pass. laura.sessions.grade -> forAll (g|g.betterThan(Grade.pass)) • union (+), intersection (*), difference (-) //the courses taught by either laura.sessions.course + marty.sessions.course //the courses taught by both laura.sessions.course * marty.sessions.course //the course taught by Laura that are not taught by Marty laura.session.course - marty.sessions.course CS551 - Lecture 8**Static Invariants**• Boolean Operators: an invariant is a Boolean expression & Quantifier (forall, exists) • and (&), or (|), a implies b (a ==> b), not a (!a), • aSet -> forall (x|P(x)) is equivalent to x:aSet::P(x), • aSet -> exists (x|P(x)) is equivalent to exist x:aSet, P(x) • Context Operator(::); short for an explicit forall // a session has an evaluation exactly when it is completed. • inv Session::self.completed = (self.eval <> null) • inv Session -> forall (self | self.completed = (self.eval <> null)) CS551 - Lecture 8**Boolean Operators**CS551 - Lecture 8**Dictionary**• The collected set of definitions of modeling constructs. • The definitions must include • the formal modeling and specification bits (relating the formal names and symbols to each other) • the (usually informal) description that relate the symbols and names to things in the problem domain. • Dictionary definitions are scoped according to package scope rules. CS551 - Lecture 8**A Typical Dictionary**CS551 - Lecture 8**Static Model: Summary**• Describes the state of the business or the component(s) we are interested in, with a set of attributes, together with an invariant, constitutes the static part of a type model. • each concept is described with a type • its state is described with attributes and associations • The invariant express constraints on the state: combinations of values that should always be observed. • To provide a vocabulary in which to describe actions, which include interactions in a business, between user and software, or between objects inside the software. • Snapshots are used to represent specific situations, and helps to develop the static model. CS551 - Lecture 8