Relational Model. Nisa ul Hafidhoh

Transcription

1 Relational Model Nisa ul Hafidhoh

2 Data Model Collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints Example of Data Model Type: Record based: Hierarchical Model Network Model Relational Model Object oriented Physical Relational Model - NH2016 2

3 Relational Database A relational database uses a collection of tables consist of row and column to give representation of data. customer_name customer_street customer_city attributes (or columns) Jones Smith Curry Lindsay Main North North Park Harrison Rye Rye Pittsfield tuples (or rows) customer Relational Model - NH2016 3

4 Example of Relational Database DB2 -> IBM ORACLE -> Oracle SYBASE -> Powersoft INFORMIX -> Informix Microsoft Access -> Microsoft Relational Model - NH2016 4

5 Structure of Relational Database Relation is used to refer to a table Tuple is used to refer to a row represents a relationship among a set of values Attribute refers to a column of a table Relation instance to refer to a specific instance of a relation, i.e., containing a specific set of rows Relational Model - NH2016 5

6 Attribute Type The set of allowed values for each attribute is called the domain of the attribute Attribute values are (normally) required to be atomic; that is, indivisible The null value is a special value that signifies that the value is unknown or does not exist The null value cause a number of difficulties when we access or update the database Relational Model - NH2016 6

7 Database Schema Database schema: the logical design of the database Database instance: snapshot of the data in the database at a given instant in time A database consists of multiple relations Information about an enterprise is broken up into parts instructor, student, advisor Bad design: univ (instructor -ID, name, dept_name, salary, student_id,..) results in repetition of information (e.g., two students have the same instructor) the need for null values (e.g., represent an student with no advisor) Relational Model - NH2016 7

8 Relation Schema A 1, A 2,, A n are attributes R = (A 1, A 2,, A n ) is a relation schema Example: instructor = (ID, name, dept_name, salary) An element of is a tuple, represented by a row in a table Order of tuples is irrelevant (tuples may be stored in an arbitrary order) Instructo relation with unordered tuples Relational Model - NH2016 8

9 How tuples within a given relation are distinguished? Relational Model - NH2016 9

10 Key Let K R K is a superkey of R if values for K are sufficient to identify a unique tuple of each possible relation r(r) Example: {ID} and {ID,name} are both superkeys of instructor. Superkey K is a candidate key if K is minimal Example: {ID} is a candidate key for Instructor One of the candidate keys is selected to be the primary key. which one? Unique, never/rarely change Foreign key constraint: Value in one relation (r1) must appear in another relation (r2) Referencing relation Referenced relation Relational Model - NH

11 Case Study: University Database A university organization may have several such record types, including - department, with fields dept name, building, and budget - course, with fields course id, title, dept name, and credits - student, with fields ID, name, dept name, and tot_cred - instructor, with fields ID, name, dept_name, salary Instructor become the advisor of students. A course may has prereqeuiste class. A section exists for a course, it must be taught by at least one instructor; however, it could possibly be taught by more than one instructor. We would require that if a particular (course id, sec id, semester, year) combination appears in section, then the same combination must appear in teaches. More than one instructor may teach one such section. A section correspondent with timeslot and classroom. Relational Model - NH

12 Schema Diagram Each relation appears as a box, with the relation name at the top The attributes listed inside the box. Primary key attributes are shown underlined. Foreign key dependencies appear as arrows from the foreign key attributes of the referencing relation to the primary key of the referenced relation. Relational Model - NH

13 Example of Schema Diagram Relational Model - NH

14 Schema of University Database department(dept name, building, budget) course(course id, title, dept name, credits) instructor(id, name, dept name, salary) student(id, name, dept name, tot cred) classroom(building, room number, capacity) prereq(course id, prereq id) section(course id, sec id, semester, year, building, room number, time slot id) teaches(id, course id, sec id, semester, year) takes(id, course id, sec id, semester, year, grade) advisor(s ID, i ID) time slot(time slot id, day, Relational start Model - time, NH2016 end time) 14

15 Schema Diagram Relational Model - NH

16 Assignment Every plagiarism is prohibited! Due date is The assignment should be delivered to Relational Model - NH

17 Assignment: Case Study Identify the relational schema and draw the diagram schema of the description bellow: A furniture company sells a number of different furniture products. These products are grouped into several product lines. The identifier for a product is Product ID, whereas the identifier for a product line is Product Line ID. We identify the following additional attributes for product: Product Description, Product Finish, and Product Standard Price. Another attribute for product line is Product Line Name. A product line may group any number of products but must group at least one product. Each product must belong to exactly one product line. Relational Model - NH

18 Assignment: Case Study [2] Customers submit orders for products. The identifier for an order is Order ID, and another attribute is Order Date. A customer may submit any number of orders, but need not submit any orders. Each order is submitted by exactly one customer. The identifier for a customer is Customer ID. Other attributes include Customer Name, Customer Address, and Customer Postal Code. A given customer order must request at least one product and only one product per order line item. Any product sold by Pine Valley Furniture may not appear on any order line item or may appear on one or more order line items. An attribute associated with each order line item is Ordered Quantity. Relational Model - NH

19 Referensi Silberschatz, Abraham; Korth, Henry F.; Sudarshan, S. ; Database System Concepts, 5 rd edition, McGraw-Hill, Ramakrishnan, Raghu; Gehrke, Johannes.; Database Management Systems, 3 rd edition, McGraw-Hill Higher Education, Date, C.J.; An Introduction to Database System, Addison Wesley Publishing Company, Vol. 7, New York, Relational Model - NH

20 Thank You Relational Model - NH