(资料库系统)

1、1,Database Systems(資料庫系統),9/27 10/1, 2007 Lecture #2,2,Course Administration,Office Hour: Thur 2-3 Can everyone get the textbook? HW #1 will be on the course homepage later today It is due 2 weeks from today. Next week reading: R each of the following situations concerns the Teaches relationship set

2、. For each situation, draw an ER diagram that describes it. Professors can teach the same course in several semesters, and each offering must be recorded.,26,Professors can teach the same course in several semesters, and only the most recent such offering needs to be recorded. Every professor must t

3、each some courses,27,Every professor teaches exactly one course (no more, no less) Every professor teaches exactly one course (no more, no less), and every course must be taught by some professor,28,Exercise 2.3 (R-G Book),Professors have an SSN, a name, an age, a rank, and a research specialty. Pro

4、jects have a project number, a sponsor name (e.g., NSF), a starting date, an ending date, and a budget.,29,Graduate students have an SSN, a name, an age, and a degree program Each project is managed by exactly one professor (known as PI) Each project is worked in by one or more professors (known as

5、Co-PIs) Each project is worked on by one or more graduate students (known as RAs),30,When graduate students work on a project, a professor must supervise their work on the project. Graduate students can work on multiple projects, in which case they will have a potentially different supervisor for ea

6、ch project. Departments have a department number, a department name, and a main office. Department has a professor (known as Chairman) who runs the department.,31,Professors work in one or more departments, and for each department that they work in, a time percentage is associated with their job Gra

7、duate students have one major department in which they are working on their degree. Each graduate student must have another, more senior graduate student as an advisor.,32,Summary,ER model is popular for conceptual design Sketch the design of a database informally using pictures Basic constructs in

8、ER model: entities, relationships, and attributes (of entities and relationships). Some additional constructs: weak entities, ISA hierarchies, and aggregation. Several kinds of integrity constraints: key constraints, participation constraints, and overlap/covering constraints for ISA hierarchies. De

9、sign guideline in ER model,33,Ubicomp Project of the Week:Hyperdragging (SONY CSL, 1999),How to bring human computer interaction (desktop PC) into the physical environment (just a bit)? “Disappearing computing”,34,Entity Sets Versus Attributes,Modeling a concept with a new entity set should satisfy

10、at least one of the following conditions: It is more than the name of something; it has at least one nonkey attribute. or It is the “many” in a many-one or many-many relationship.,35,Example: Okay,Beers,Manfs,ManfBy,name,Manfs deserves to be an entity set because of the nonkey attribute addr. Beers

11、deserves to be an entity set because it is the “many” of the many-one relationship ManfBy.,name,addr,36,Example: Beers Entity not Needed,Beers,Manfs,ManfBy,name,Beers can be an attribute rather than an entity.,name,addr,37,Example: Okay,Beers,name,There is no need to make the manufacturer an entity set, because we record nothing about manufacturers besides their name.,m