پاورپوینت کامل Chapter 9: Object-Based Databases 36 اسلاید در PowerPoint

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پاورپوینت کامل Chapter 9: Object-Based Databases 36 اسلاید در PowerPoint

اسلاید ۴: Complex Data TypesMotivation:Permit non-atomic domains (atomic indivisible)Example of non-atomic domain: set of integers,or set of tuplesAllows more intuitive modeling for applications with complex dataIntuitive definition:allow relations whenever we allow atomic (scalar) values — relations within relationsRetains mathematical foundation of relational model Violates first normal form.

اسلاید ۵: Example of a Nested RelationExample: library information systemEach book has title, a set of authors,Publisher, anda set of keywordsNon-1NF relation books

اسلاید ۶: ۴NF Decomposition of Nested RelationRemove awkwardness of flat-books by assuming that the following multivalued dependencies hold:title authortitle keywordtitle pub-name, pub-branchDecompose flat-doc into 4NF using the schemas:(title, author )(title, keyword )(title, pub-name, pub-branch )

اسلاید ۷: ۴NF Decomposition of flat–books

اسلاید ۸: Problems with 4NF Schema4NF design requires users to include joins in their queries.1NF relational view flat-books defined by join of 4NF relations:eliminates the need for users to perform joins,but loses the one-to-one correspondence between tuples and documents.And has a large amount of redundancyNested relations representation is much more natural here.

اسلاید ۹: Complex Types and SQL:1999Extensions to SQL to support complex types include:Collection and large object typesNested relations are an example of collection typesStructured typesNested record structures like composite attributes InheritanceObject orientationIncluding object identifiers and referencesOur description is mainly based on the SQL:1999 standardNot fully implemented in any database system currentlyBut some features are present in each of the major commercial database systemsRead the manual of your database system to see what it supports

اسلاید ۱۰: Structured Types and Inheritance in SQLStructured types can be declared and used in SQL create type Name as (firstname varchar(20), lastname varchar(20)) finalcreate type Address as (street varchar(20), city varchar(20), zipcode varchar(20))not finalNote: final and not final indicate whether subtypes can be createdStructured types can be used to create tables with composite attributes create table customer (nameName,addressAddress,dateOfBirth date)Dot notation used to reference components: name.firstname

اسلاید ۱۱: Structured Types (cont.)User-defined row typescreate type CustomerType as (name Name,address Address,dateOfBirth date)not finalCan then create a table whose rows are a user-defined typecreate table customer of CustomerType

اسلاید ۱۲: MethodsCan add a method declaration with a structured type.method ageOnDate (onDate date)returns interval yearMethod body is given separately.create instance method ageOnDate (onDate date)returns interval yearfor CustomerTypebeginreturn onDate – self.dateOfBirth;endWe can now find the age of each customer:select name.lastname, ageOnDate (current_date)from customer

اسلاید ۱۳: InheritanceSuppose that we have the following type definition for people:create type Person (name varchar(20), address varchar(20))Using inheritance to define the student and teacher types create type Student under Person (degree varchar(20), department varchar(20)) create type Teacher under Person (salary integer, department varchar(20))Subtypes can redefine methods by using overriding method in place of method in the method declaration

اسلاید ۱۴: Multiple InheritanceSQL:1999 and SQL:2003 do not support multiple inheritanceIf our type system supports multiple inheritance, we can define a type for teaching assistant as follows: create type Teaching Assistant under Student, TeacherTo avoid a conflict between the two occurrences of department we can rename them create type Teaching Assistant under Student with (department as student_dept ), Teacher with (department as teacher_dept )