軟件需求分析英文課件：Chap 6 - Database Design

1、1Chapter 6 Database Designw The Relational Data Model and Object Modelw Persistence Frameworksw Database Design2The Relational Data Model and Object Model36.1 The Relational Data Model and Object Modelw The Relational Data Modelw The Object Model4The Relational Data Model ORDERLINE ITEMPRODUCTOrder_

2、IdLineItem_IdDescriptionPriceQuantityProduct_IdOrder_IdProduct_IdNamePricelineItemorderproductslineItemsRelationColumnsEntityw Relational model is composed of Entities An entity may be a physical table or a logical projection of several tables also known as a view.Relations5The Object Modelw The Obj

3、ect Model is composed of Classes (attributes)AssociationsLineItem- quantity : Integer- number : Integer1.*+lineItemsOrder- number : Integer+orderProduct- number : Integer- description : String- unitPrice : Double1Software Product- version : DoubleHardware Product- assembly : String6w RDBMS and Objec

4、t Orientation are not entirely compatible RDBMS Focus is on data Better suited for ad-hoc relationships and reporting application Expose data (column values) Object Oriented system Focus is on behavior Better suited to handle state-specific behavior where data is secondary Hide data (encapsulation)R

5、elational Databases and Object Orientation7The Persistence Frameworks 86.2 Persistence Frameworks w Persistence Framework w Hibernate9Persistence Frameworksw The challenge: Changes should not break the modelw The solution: An object-relational framework that Encapsulates the physical data store Prov

6、ides object translation servicesw The importance of the framework 30% of development time is spent in accessing an RDBMS Maintenance can be 60% of total costBusiness Object ModelRelational DatabaseCompact interfacesObject-relational translationEncapsulates data store10Hibernate w Object / Relational

7、 mapping (ORM) and persistence / query framework i.e. It does even more stuff for you!w Some features of Hibernate HibernateDaoSupport superclass, easy HibernateTemplate access Database independence - sits between the database and your java code, easy database switch without changing any code Object

8、 / Relational Mapping (ORM) - Allows a developer to treat a database like a collection of Java objects Object 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”

9、 of Java objects) Hibernate Mapping - Uses HBM XML files to map value objects (POJOs) to database tables Transparent persistence - Allows easy saves/delete/retrieve for simple value objects Very high performance “in general” due to intelligent (2-level) caching, although in a few cases hand-written

10、SQL might beat it11Hibernatew Hibernate basically sits between the DB and your codew Can map persistent objects to tables12Database Design136.3 Database Designw Purposew Overvieww Steps Map persistent design classes to tables Modeling Associations in the Data Model Modeling Aggregation in the Data M

11、odel Modeling Inheritance in the Data Model Distribute class behavior to the database14Purpose qTo ensure that persistent data is stored consistently and efficiently. qTo define behavior that must be implemented in the database. 15Database Design OverviewSupplementarySpecificationsDatabaseDesignUse-

12、Case RealizationDesignGuidelinesData Model16Mapping Persistent Classes to Tablesw In a relational databaseEvery row is regarded as an objectA column in a table is equivalent to a persistent attribute of a classStudent- name : String- address : String- studentID : LongNameStudent_IDThomas Stuart12345

13、6Object InstanceAttributes from object type17Modeling Associations in the Data Model w Associations between two persistent objects are realized 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_ID678

14、456789NameDescriptionNumberMath 101Algebra456789Course Offering tableCourse tableCourse- name- description- numberCourseOffering- number : String 0.*0.*1Primary KeyForeign Key18Modeling Aggregation in the Data Modelw Aggregation is also modeled using foreign key relationshipsUsing composition implem

15、ents a cascading delete constraintStudent.- studentID : intSchedule- semester : Semester0.*10.*1Student_IDSemester123456Spring 2001Schedule tableStudent_ID123456Foreign KeyPrimary KeyStudent table19Modeling Inheritance in the Data Modelw A data model does not support modeling inheritance in a direct

16、 wayw Two optionsUse separate tables (normalized data)Duplicate all inherited associations and attributes (de-normalized data)20Modeling Inheritance in the Data Model - Example21Modeling Inheritance in the Data Model - Example22Modeling Inheritance in the Data Model - Example23Map Class Behavior to

17、Stored Proceduresw Determine if any operations can be implemented as a stored procedurew Candidate operationsDeal with persistent data Any operations where a query is involved in a computationNeed to access the database to validate data24What Are Stored Procedures?w A stored procedure is executable

18、code which runs under the RDBMSw Two types of stored proceduresProcedures: Executed explicitly by an applicationTriggers: Invoked implicitly when some database event occurs25Example: Map Class Behavior to Stored ProceduresStudent.+ getTuition()+ addSchedule()+ getSchedule()+ deleteSchedule()+ hasPrerequisites()# passed() + getNextAvailID()+ getStudentID()+ getName()+ getAd