CMPT 354 Database Systems I

Transcription

1 CMPT 354 Database Systems I Chapter 4.6 Kifer Reference Book UML (Unified Modeling Language) Class Modeling

2 UML Introduction UML (Unified Modeling Language) is a set of specifications for software engineering and business processes. The current version is UML 2.0. UML is maintained by the OMG (Object Modeling Group) at The class diagram is one of six structure diagrams, or nine diagrams in total. The class diagram is similar to E-R diagrams, and used to model databases, but is designed to model software components in general.

3 UML Class Diagrams Chapter 4.6 in Database Systems: an applicationoriented approach/kiefer, Bernstein, Lewis. UML Class Diagrams are object-oriented. A class is equivalent to an entity set in E-R modeling, and an instance of the class is an object. Main visual difference is: members are written inside the drawn rectangle. Main advantages: Class methods/operations, more expressive constraints. Main disadvantages: Lacking some database specific expressions.

4 UML Classes Each attribute has a domain constraint! Classes have associated methods. Function have return type constraint as well. Function parameters are optionally classified as [in] or [out]. [in] is default. Clients SSN: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():char(255) Moved([in] newaddr:char(255))

5 UML Associations An association is equivalent to relationships in E-R. Binary associations are drawn with a simple link. Multiway relationships are drawn with a diamond. A link can have a name, multiplicity, and roles. Clients SSN: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) 1..3 hold * owners holdings 1 primary joint 0..2 joint account Account#: int Balance: real = 0

6 Association Classes Associations can have attributes as well. Attributes are created using a special association class, and linked via a dashed line. hold joindate: Date Clients SSN: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) 1..3 hold * owners holdings Account#: int Balance: real = 0

7 Multiway Associations hold join date: Date 1 branch bid: int Location: String Clients SSN: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) hold 1..3 owners * holdings Account#: int Balance: real

8 Keys UML does not specify how to represent keys. However, UML allows extensions through prototypes. Prototypes are notation conventions agreed upon by groups using UML for a project. The prototype name is enclosed in <<pname>>. UML profiles specify UML notation including prototypes that are needed for the target community. No standardized UML profile for databases. We will use (from rational): <<pk>>,<<fk>> to denote primary and foreign key. <<unique>> to denote single value constraint. <<check>>,<<trigger> for checks and triggers.

9 UML Keys Example hold join date: Date Clients SSN: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) 1..3 hold * owners holdings Account#: int Balance: real = 0

10 UML Keys Example hold join date: Date Clients <<pk>>ssn: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) 1..3 hold * owners holdings <<pk>>account#: int Balance: real = 0

11 UML Keys Example Hold <<fk>>ssn: int <<fk>>account#: int join date: Date Clients <<pk>>ssn: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) 1..3 hold * owners holdings <<pk>>account#: int Balance: real = 0

12 UML Foreign Keys Example Clients <<pk>>ssn: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) 1 hold * owners holdings primary joint joint account <<pk>>account#: int Balance: real = 0

13 UML Foreign Keys Example Clients <<pk>>ssn: int Name: char(255) Address: char(255) Phone: char(10) GetSurname():String Moved(newAddr:String) 1 hold * owners holdings primary joint joint account <<pk>>account#: int <<fk>>ssn: int Join date: Date Balance: real = 0

14 Inheritance UML allows class hierarchies using generalization similarly to isa in E-R. A generalization is Drawn as a hollow arrow. Notation can be straight arrows, or tree style connectivity. Can specify covering and overlap constraints directly. A covering constraint uses the keyword complete. An overlap constraint uses the keyword disjoint. The constraints are specified within curly braces.

15 Inheritance Example <<PK>>Account#: int Balance: real = 0 {complete, disjoint} Chequing ATMCard#: int Trans#: int Savings Interest: real

16 Part-of Relationships UML has a special part-of relationship called aggregation, used to denote objects that can be a part of other objects. Aggregation is a non-exclusive relationship. Note: different from E-R aggregation. Drawn with a hollow diamond on the aggregate class. Need to assign multiplicity. What is the restriction? Programs <<pk>>program: String * 15..* Courses <<pk>>course_id: char(8) <<pk>>section: char(6)

17 Exclusive Part-of Relationships An exclusive part-of relationship is called composition. Objects that are part of other objects cannot exist without the whole existing. A composition is a different type of aggregation. Drawn with a filled diamond on the compositing class. Need to assign multiplicity. What is the restriction? <<PK>>Account#: int Balance: real = Mortgage <<pk>>type: string amount: real

18 UML Conclusion UML class diagrams can be used to model database systems. Only one UML tool even in a Database design life cycle. (others include: use case diagrams, sequence diagrams, and activity diagrams) Class diagrams are an object oriented approach that lends itself to implementation. Can be applied to object oriented databases, or relational databases, similarly to E-R diagrams.