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Database System Concepts, 6 th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-usewww.db-book.com Chapter 2: Intro to Relational Model

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©Silberschatz, Korth and Sudarshan2.2Database System Concepts - 6 th Edition Chapter 1: Introduction Part 1: Relational databases Chapter 2: Introduction to the Relational Model Chapter 3: Introduction to SQL Chapter 4: Intermediate SQL Chapter 5: Advanced SQL Chapter 6: Formal Relational Query Languages Part 2: Database Design Chapter 7: Database Design: The E-R Approach Chapter 8: Relational Database Design Chapter 9: Application Design Part 3: Data storage and querying Chapter 10: Storage and File Structure Chapter 11: Indexing and Hashing Chapter 12: Query Processing Chapter 13: Query Optimization Part 4: Transaction management Chapter 14: Transactions Chapter 15: Concurrency control Chapter 16: Recovery System Part 5: System Architecture Chapter 17: Database System Architectures Chapter 18: Parallel Databases Chapter 19: Distributed Databases Database System Concepts Part 6: Data Warehousing, Mining, and IR Chapter 20: Data Mining Chapter 21: Information Retrieval Part 7: Specialty Databases Chapter 22: Object-Based Databases Chapter 23: XML Part 8: Advanced Topics Chapter 24: Advanced Application Development Chapter 25: Advanced Data Types Chapter 26: Advanced Transaction Processing Part 9: Case studies Chapter 27: PostgreSQL Chapter 28: Oracle Chapter 29: IBM DB2 Universal Database Chapter 30: Microsoft SQL Server Online Appendices Appendix A: Detailed University Schema Appendix B: Advanced Relational Database Model Appendix C: Other Relational Query Languages Appendix D: Network Model Appendix E: Hierarchical Model

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©Silberschatz, Korth and Sudarshan2.3Database System Concepts - 6 th Edition Chapter 2: Intro to Relational Model 2.1 Structure of Relational Databases 2.2 Database Schema 2.3 Keys 2.4 Schema Diagrams 2.5 Relational Query Languages 2.6 Relational Operations

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©Silberschatz, Korth and Sudarshan2.4Database System Concepts - 6 th Edition Example of a Relation attributes (or columns) tuples (or rows)

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©Silberschatz, Korth and Sudarshan2.5Database System Concepts - 6 th Edition Attribute Types 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 special value null is a member of every domain The null value causes complications in the definition of many operations

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©Silberschatz, Korth and Sudarshan2.6Database System Concepts - 6 th Edition Relation Schema and Instance 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) Formally, given sets D 1, D 2, …. D n a relation r is a subset of D 1 x D 2 x … x D n Thus, a relation is a set of n-tuples (a 1, a 2, …, a n ) where each a i D i The current values (relation instance) of a relation are specified by a table An element t of r is a tuple, represented by a row in a table

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©Silberschatz, Korth and Sudarshan2.7Database System Concepts - 6 th Edition Relations are Unordered Order of tuples is irrelevant (tuples may be stored in an arbitrary order) Example: instructor relation with unordered tuples

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©Silberschatz, Korth and Sudarshan2.8Database System Concepts - 6 th Edition Database 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) Normalization theory (Chapter 7) deals with how to design “good” relational schemas

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©Silberschatz, Korth and Sudarshan2.9Database System Concepts - 6 th Edition Keys 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? Foreign key constraint: Value in one relation must appear in another Referencing relation Referenced relation

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©Silberschatz, Korth and Sudarshan2.10Database System Concepts - 6 th Edition Schema Diagram for University Database

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©Silberschatz, Korth and Sudarshan2.11Database System Concepts - 6 th Edition Relational Query Languages Procedural vs.non-procedural, or declarative “Pure” languages: Relational algebra Tuple relational calculus Domain relational calculus Relational operators

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©Silberschatz, Korth and Sudarshan2.12Database System Concepts - 6 th Edition Selection of tuples Relation r Select tuples with A=B and D > 5 σ A=B and D > 5 (r)

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©Silberschatz, Korth and Sudarshan2.13Database System Concepts - 6 th Edition Selection of Columns (Attributes) Relation r: Select A and C Projection Π A, C (r)

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©Silberschatz, Korth and Sudarshan2.14Database System Concepts - 6 th Edition Joining two relations – Cartesian Product Relations r, s: r x s:

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©Silberschatz, Korth and Sudarshan2.15Database System Concepts - 6 th Edition Union of two relations Relations r, s: r s:

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©Silberschatz, Korth and Sudarshan2.16Database System Concepts - 6 th Edition Set difference of two relations Relations r, s: r – s:

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©Silberschatz, Korth and Sudarshan2.17Database System Concepts - 6 th Edition Set Intersection of two relations Relation r, s: r s

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©Silberschatz, Korth and Sudarshan2.18Database System Concepts - 6 th Edition Joining two relations – Natural Join Let r and s be relations on schemas R and S respectively. Then, the “natural join” of relations R and S is a relation on schema R S obtained as follows: Consider each pair of tuples t r from r and t s from s. If t r and t s have the same value on each of the attributes in R S, add a tuple t to the result, where t has the same value as t r on r t has the same value as t s on s

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©Silberschatz, Korth and Sudarshan2.19Database System Concepts - 6 th Edition Natural Join Example Relations r, s: Natural Join r s

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©Silberschatz, Korth and Sudarshan2.20Database System Concepts - 6 th Edition Figure in-2.1

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Database System Concepts, 6 th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-usewww.db-book.com End of Chapter 2

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©Silberschatz, Korth and Sudarshan2.22Database System Concepts - 6 th Edition Figure 2.01

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©Silberschatz, Korth and Sudarshan2.23Database System Concepts - 6 th Edition Figure 2.02

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©Silberschatz, Korth and Sudarshan2.24Database System Concepts - 6 th Edition Figure 2.03

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©Silberschatz, Korth and Sudarshan2.25Database System Concepts - 6 th Edition Figure 2.04

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©Silberschatz, Korth and Sudarshan2.26Database System Concepts - 6 th Edition Figure 2.05

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©Silberschatz, Korth and Sudarshan2.27Database System Concepts - 6 th Edition Figure 2.06

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©Silberschatz, Korth and Sudarshan2.28Database System Concepts - 6 th Edition Figure 2.07

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©Silberschatz, Korth and Sudarshan2.29Database System Concepts - 6 th Edition Figure 2.10

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©Silberschatz, Korth and Sudarshan2.30Database System Concepts - 6 th Edition Figure 2.11

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©Silberschatz, Korth and Sudarshan2.31Database System Concepts - 6 th Edition Figure 2.12

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©Silberschatz, Korth and Sudarshan2.32Database System Concepts - 6 th Edition Figure 2.13

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