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HW 1B Chapter 8 Define the following terms superclass of a subclass superclass subclass relationship IS A 8 2 relationship specialization generalization category specific local attributes and specific relationships Superclass of a subclass is an entity type which has a subgrouping of entities that have additional specific attributes and or relationships Superclass subclass relationship is the relationship between superclass and one of its subclasses A subclass cannot exist on its own so this relationship is mandatory for every subclass IS A relationship is another name for superclass subclass relationship that is often used when Instead of saying BOOK and NOVEL entity types participate in referring to the concept superclass subclass relationship we could simply say NOVEL IS A BOOK Specialization is the procedure of creating a set of subclasses based on their differences for the particular entity that becomes the superclass Generalization is the procedure of creating a single superclass for several different entity types based on common attributes or relationships Entity types that are generalized become subclasses of the created superclass Category is a subclass which represents a collection of entities of different types Category is a subset of the union of entity sets of different entity types It can be total or partial Total category has a superclass that is union of all entity types while partial category has a subset of the union as its superclass Specific local attributes are attributes that can be found in subclasses and cannot be found in superclasses They are optional and are used to distinguish specific subclasses from other subclasses Specific relationships are relationship types in which only the specific subclass or subclasses can participate in The superclass is not allowed to participate in specific relationships and like specific attributes they are optional 8 3 Discuss the mechanism of attribute relationship inheritance Why is it useful Attribute inheritance mechanism can be noticed when dealing with superclass and subclass concepts The general rule is that the subclass inherits all the attributes and relationships from its superclass but there are some special cases so here is a brief description of attribute relationship inheritance mechanisms Type inheritance Entity that is a member of a subclass inherits all attributes and relationships from its superclass but can also have additional attributes and relationships specific local This way a subclass can be viewed as an entity of its own Hierarchies single inheritance In specialization hierarchy there is a rule that every entity type can participate as a subclass in only one class subclass relationship This means that a subclass can be a subclass of a superclass once but that same subclass can be superclass to any number of other subclasses In this case the subclass inherits all the attributes and relationships from direct and indirect superclasses all the way to the root of hierarchy Lattices multiple inheritance In specialization lattice a single subclass can have more than one superclass Every attribute and relationship that can be found in any of the superclasses is inherited to subclass There is a rule of uniqueness that states that every attribute must be inherited only once Example Let s say there are entity types PERSON LIBRARIAN ARCHIVIST and DIRECTOR in the Library database PERSON is a superclass and has two subclasses LIBRARIAN and ARCHIVIST To be a DIRECTOR one must have experience with archiving and regular library jobs so a DIRECTOR is a shared subclass between ARCHIVIST and LIBRARIAN DIRECTOR entity type inherits all attributes from ARCHIVIST LIBRARIAN and PERSON entity types with constraint that if some attribute appears more than once it is inherited just once so no duplicate attributes exist Attribute inheritance mechanism is useful because there is no need for duplicating the same type of attributes and relationships Database schema looks more concise and it is easier to locate attributes and relationships when we understand the concept of inheritance Discuss user defined and attribute defined specializations and identify the differences between 8 5 the two User defined specializations are specializations in which the user chooses how to sort entity instances into subclasses User decides the sorting criteria however he she pleases Attribute defined specializations are specializations the subclasses are predicate defined and the membership condition for all subclasses is on the same defining superclass attribute in which all User defined specializations Attribute defined specializations Membership specialization cannot be decided automatically user defined of defined Membership of attribute defined specialization can be decided automatically The user is responsible for identifying proper subclass The value of the same attribute is used in defining predicate for all subclasses 8 19 Identify all the important concepts represented in the library database case study described below In particular identify the abstractions of classification entity types and relationship types aggregation identification and specialization generalization Specify min max cardinality constraints whenever possible List details that will affect the eventual design but that have no bearing on the conceptual design List the semantic constraints separately Draw an EER diagram of the library database In the given case study we deal with 4 types of abstractions Classification Aggregation Identification specialization generalization CLASSIFICATION Entity types BOOK ISBN Title Author multivalued Language multivalued Edition Binding Description Subject area multivalued No of copies MEMBER SSN Name Campus addr Home addr multivalued Phone no multivalued CARD Card no Valid until LIBRARIAN SSN Name Salary Relationship types CHECKS OUT Time to return This is a ternary relationship type that relates MEMBER LENDABLE book and CHECK OUT librarian Member can check out up to 5 books at the same time All entity types participating in this relationship have partial participation constraint meaning it is not necessary to check out MAILES Date This ternary relationship type relates ASSISTANT CARD and FACULTY member Not every card has to be mailed and not every assistant has to mail a card so only the FAULTY member has a total participation constraint for participating in this relationship GETS Date This ternary relationship type relates

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UTD CS 6360 - Chapter 8 HW

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