Slide 1

Database Design Some of these slides are derived from IBM/Rational slides from courses on UML and object-oriented design and analysis. Copyright to the original slides resides with IBM/Rational. They are used here, in this course, under password protection limited to students enrolled in the course, with permission of the owners, but are not to be published or further distributed. Other slides are derived from Dennis, Wixom & Tegarden Systems Analysis & Design with UML, 3 rd edition, copyright John Wiley & Sons, used under similar permissions. Slide 2 Objectives: Database Design Define the purpose of Database Design and where in the lifecycle it is performed Explain how persistent classes map to the data model Learn how to distribute class behavior to the database Slide 3 Database Design in Context [Early Elaboration Iteration] [Inception Iteration (Optional)] Define a Candidate Architecture Perform Architectural Synthesis Analyze Behavior Refine the Architecture Design Components Design the Database (Optional) Database Design Database Designer Slide 4 Database Design Overview Supplementary Specifications Database Design Use-Case Realization Project Specific Guidelines Analysis Classes Design Classes Design ModelData Model Slide 5 Database Design Steps Map persistent design classes to the data model Distribute class behavior to the database Slide 6 Database Design Steps Map persistent design classes to the data model Distribute class behavior to the database Slide 7 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) Relational Databases & Object Orientation Slide 8 The Relational Data Model Relational model is composed of Entities Attributes Relations ORDERLINE ITEM PRODUCT Order_Id LineItem_Id Description Price Quantity Product_Id Order_Id Product_Id Name Price lineItem order products lineItems Entity Relation Columns (aka Attributes) An ERD diagramAn ERD diagram Slide 9 The Object Model The Object Model is composed of Classes Attributes Associations LineItem - quantity : Integer - number : Integer 1..* +lineItems Order - number : Integer +order Product - number : Integer - description : String - unitPrice : Double 1 Software Product - version : Double Hardware Product - assembly : String A class diagram Slide 10 Persistence Frameworks Challenge: Changes should not break the model Solution: an object-relational framework that Encapsulates the physical data store Provides object translation services Importance of the framework 30% of development time is spent in accessing an RDBMS Maintenance can be 60% of total cost Business Object Model Relational Database Compact interfaces Object-relational translation Encapsulates data store Slide 11 Object-Relational Framework: Characteristics Performance Decomposing objects to data Composing objects from data Minimize design compromises Limit changes to object and relational models Make it extensible 15%-35% of the application will require extensions to the framework Slide 12 Object-Relational Frameworks: Characteristics (continued) Documentation of the API Documentation of internals, for extension Support for common object-relational mappings Persistence interfaces Examples are save, delete, and find Slide 13 Common Object-Relational Services Patterns are beginning to emerge for object-relational applications CORBA Services specification Persistence Query - e.g., find, find unique Transactions Concurrency Relationships Refer to the appropriate CORBA specifications for further details. Slide 14 Student - name : String - address : String - studentID : Long Mapping Persistent Classes to Tables In a relational database Every row is regarded as an object A column in a table is equivalent to a persistent attribute of a class NameAddressStudent_ID Thomas Stuart987 High St.123456 Object Instance Attributes from object type Slide 15 Mapping Associations Between Persistent Objects Associations between two persistent objects are realized as foreign keys to the associated objects. A foreign key is a column in one table that contains the primary key value of associated object NumberCourse_ID 678456789 NameDescriptionNumber Math 101Algebra456789 Course Offering table Course table Course - name - description - number CourseOffering - number : String 0..* 1 Primary Key Foreign Key Slide 16 Mapping Aggregation to the Data Model Aggregation is also modeled using foreign key relationships The use of composition implements a cascading delete constraint Student. - studentID : int Schedule - semester : Semester 0..* 1 Student_IDSemester 123456Spring 2001 Schedule table Student_ID 123456 Foreign Key Primary Key Student table Slide 17 Modeling Inheritance in the Data Model A Data Model does not support modeling inheritance in a direct way Two options: Use separate tables (normalized data) Duplicate all inherited associations and attributes (de-normalized data) Slide 18 Database Design Steps Map persistent design classes to the data model Distribute class behavior to the database Slide 19 What Are Stored Procedures? A stored procedure is executable code that runs under the RDBMS Two types of stored procedures: Procedures: Executed explicitly by an application Triggers: Invoked implicitly when some database event occurs Slide 20 Map Class Behavior to Stored Procedures Determine if any operations can be implemented as a stored procedure Candidates: Operations that deal with persistent data Operations in which a query is involved in a computation Operations that need to access the database to validate data Slide 21 Example: Map Class Behavior to Stored Procedures Student. + getTuition() + addSchedule() + getSchedule() + deleteSchedule() + hasPrerequisites() # passed() + getNextAvailID() + getStudentID() + getName() + getAddress() ClassCandidate Operations getTuition addSchedule getSchedule deleteSchedule getStudentID getName getAddress Slide 22 Checkpoints: Database Design Have all persistent classes been mapped to database structures? Have stored procedures and triggers been defined? Does the persistence mechanism use stored procedures and database triggers consistently? Slide 23 Review: Database Design What is the purpose of the Database Design? What comprises a relational data model? What are the components of an object model? When mapping persistent classes to tables, what is every row in a table regarded as? What is every column equivalent to? What are stored procedures?