软件需求分析英文课件：Chap 6 - Database Design

1、Chapter 6 Database Design The Relational Data Model and Object Model Persistence Frameworks Database DesignThe Relational Data Model and Object Model6.1 The Relational Data Model and Object Model The Relational Data Model The Object ModelThe Relational Data Model ORDERLINE ITEMPRODUCTOrder_IdLineIte

2、m_IdDescriptionPriceQuantityProduct_IdOrder_IdProduct_IdNamePricelineItemorderproductslineItemsRelationColumnsEntityRelational model is composed of EntitiesAn entity may be a physical table or a logical projection of several tables also known as a view.RelationsThe Object ModelThe Object Model is co

3、mposed of Classes (attributes)AssociationsLineItem- quantity : Integer- number : Integer1.*+lineItemsOrder- number : Integer+orderProduct- number : Integer- description : String- unitPrice : Double1Software Product- version : DoubleHardware Product- assembly : StringRDBMS and Object Orientation are

4、not entirely compatibleRDBMS Focus is on dataBetter suited for ad-hoc relationships and reporting applicationExpose data (column values)Object Oriented systemFocus is on behaviorBetter suited to handle state-specific behavior where data is secondaryHide data (encapsulation)Relational Databases and O

5、bject OrientationThe Persistence Frameworks 6.2 Persistence Frameworks Persistence Framework HibernatePersistence FrameworksThe challenge:Changes should not break the modelThe solution: An object-relational framework thatEncapsulates the physical data storeProvides object translation servicesThe imp

6、ortance of the framework30% of development time is spent in accessing an RDBMSMaintenance can be 60% of total costBusiness Object ModelRelational DatabaseCompact interfacesObject-relational translationEncapsulates data storeHibernate Object / Relational mapping (ORM) and persistence / query framewor

7、ki.e. It does even more stuff for you!Some features of HibernateHibernateDaoSupport superclass, easy HibernateTemplate accessDatabase independence - sits between the database and your java code, easy database switch without changing any codeObject / Relational Mapping (ORM) - Allows a developer to t

8、reat a database like a collection of Java objectsObject oriented query language (HQL) - *Portable* query language, supports polymorphic queries etc.You can also still issue native SQL, and also queries by “Criteria” (specified using “parse tree” of Java objects)Hibernate Mapping - Uses HBM XML files

9、 to map value objects (POJOs) to database tables Transparent persistence - Allows easy saves/delete/retrieve for simple value objectsVery high performance “in general” due to intelligent (2-level) caching, although in a few cases hand-written SQL might beat itHibernateHibernate basically sits betwee

10、n the DB and your codeCan map persistent objects to tablesDatabase Design6.3 Database Design Purpose Overview Steps Map persistent design classes to tables Modeling Associations in the Data Model Modeling Aggregation in the Data Model Modeling Inheritance in the Data Model Distribute class behavior

11、to the databasePurpose To ensure that persistent data is stored consistently and efficiently. To define behavior that must be implemented in the database. Database Design OverviewSupplementarySpecificationsDatabaseDesignUse-Case RealizationDesignGuidelinesData ModelMapping Persistent Classes to Tabl

12、esIn a relational databaseEvery row is regarded as an objectA column in a table is equivalent to a persistent attribute of a classNameStudent_IDThomas Stuart123456Object InstanceAttributes from object typeModeling Associations in the Data Model Associations between two persistent objects are realize

13、d as foreign keys to the associated objects.A foreign key is a column in one table which contains the primary key value of associated objectNumberCourse_ID678456789NameDescriptionNumberMath 101Algebra456789Course Offering tableCourse tableCourse- name- description- numberCourseOffering- number : Str

14、ing 0.*0.*1Primary KeyForeign KeyModeling Aggregation in the Data ModelAggregation is also modeled using foreign key relationshipsUsing composition implements a cascading delete constraintStudent.- studentID : intSchedule- semester : Semester0.*10.*1Student_IDSemester123456Spring 2001Schedule tableS

15、tudent_ID123456Foreign KeyPrimary KeyStudent tableModeling Inheritance in the Data ModelA data model does not support modeling inheritance in a direct wayTwo optionsUse separate tables (normalized data)Duplicate all inherited associations and attributes (de-normalized data)Modeling Inheritance in th

16、e Data Model - ExampleModeling Inheritance in the Data Model - ExampleModeling Inheritance in the Data Model - ExampleMap Class Behavior to Stored ProceduresDetermine if any operations can be implemented as a stored procedureCandidate operationsDeal with persistent data Any operations where a query

17、is involved in a computationNeed to access the database to validate dataWhat Are Stored Procedures?A stored procedure is executable code which runs under the RDBMSTwo types of stored proceduresProcedures: Executed explicitly by an applicationTriggers: Invoked implicitly when some database event occursExample: Map Class Behavior to Stored ProceduresClass