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Chapter 2: Intro to Relational Model Database System Concepts, 6th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Database System Concepts 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 - 6th Edition 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 2.2 ©Silberschatz, Korth and Sudarshan 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 Database System Concepts - 6th Edition 2.3 ©Silberschatz, Korth and Sudarshan In The Beginning... Everything in Table Set-oriented Query Language E.F. Codd -- 1970 CACM Paper -- Turing Award 1970 4 Database System Concepts - 6th Edition 2.4 ©Silberschatz, Korth and Sudarshan Example of a Relation attributes (or columns) tuples, records (or rows) 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 Database System Concepts - 6th Edition 2.5 ©Silberschatz, Korth and Sudarshan Relation Schema and Instance A1, A2, …, An are attributes R = (A1, A2, …, An ) is a relation schema Example: instructor = (ID, name, dept_name, salary) Formally, given sets D1, D2, …. Dn a relation r is a subset of D1 x D2 x … x Dn Thus, a relation is a set of n-tuples (a1, a2, …, an) where each ai Di 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 Database System Concepts - 6th Edition 2.6 ©Silberschatz, Korth and Sudarshan Relations are Unordered Order of tuples is irrelevant (tuples may be stored in an arbitrary order) Relations are basically set! Example: the instructor relation with unordered tuples Database System Concepts - 6th Edition 2.7 ©Silberschatz, Korth and Sudarshan Database A database consists of multiple relations Information about an University enterprise is broken up into parts instructor student advisor Bad design: university (instructor -ID, name, dept_name, salary, building, budget..) 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 Database System Concepts - 6th Edition 2.8 ©Silberschatz, Korth and Sudarshan University Relation (instructor -ID, name, dept_name, salary, building, budget) Database System Concepts - 6th Edition 2.9 ©Silberschatz, Korth and Sudarshan 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 Database System Concepts - 6th Edition 2.10 ©Silberschatz, Korth and Sudarshan Schema Diagram for University Database Database System Concepts - 6th Edition 2.11 ©Silberschatz, Korth and Sudarshan Figure 2.02: The Course relation Figure 2.05: The Department Relation Figure 2.03: The Pre-requisite relation Database System Concepts - 6th Edition 2.12 Figure 2.04: The Instructor relation ©Silberschatz, Korth and Sudarshan Figure 2.06: The Section relation Figure 2.07: The Teaches relation Database System Concepts - 6th Edition 2.13 ©Silberschatz, Korth and Sudarshan Relational Query Languages Procedural vs. non-procedural (declarative) “Pure” formal query languages: Relational algebra Tuple relational calculus Domain relational calculus Relational operators Select Project Cartesian Product Set Union Set Minus Database System Concepts - 6th Edition 2.14 ©Silberschatz, Korth and Sudarshan Selection ( σ ) of tuples Relation r Select tuples with A=B and D > 5 σ A=B and D > 5 Database System Concepts - 6th Edition (r) 2.15 ©Silberschatz, Korth and Sudarshan Projection (Π) of Columns (Attributes) Relation r: Select A and C Projection Π A, C (r) Database System Concepts - 6th Edition 2.16 ©Silberschatz, Korth and Sudarshan Cartesian Product ( x ): Cross-Product two relations Relations r, s: r x s: Database System Concepts - 6th Edition 2.17 ©Silberschatz, Korth and Sudarshan Union ( ) of two relations Relations r, s: r s: Database System Concepts - 6th Edition 2.18 ©Silberschatz, Korth and Sudarshan Set difference ( – ) of two relations Relations r, s: r – s: Database System Concepts - 6th Edition 2.19 ©Silberschatz, Korth and Sudarshan Set Intersection ( ) of two relations Relation r, s: rs Database System Concepts - 6th Edition 2.20 ©Silberschatz, Korth and Sudarshan Natural Join ( ) : Joining two relations Let r and s be relations on schemas R and S respectively. The “natural join” of relations R and S is a relation on schema R S obtained as follows: Consider each pair of tuples tr from r and ts from s. If tr and ts 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 tr on r t has the same value as ts on s Relations r, s: Natural Join Database System Concepts - 6th Edition r s 2.21 ©Silberschatz, Korth and Sudarshan Some of Relational Algebra Operators: Figure in-2.1 Database System Concepts - 6th Edition 2.22 ©Silberschatz, Korth and Sudarshan Figure 2.02: The Course relation Figure 2.05: The Department Relation Figure 2.03: The Pre-requisite relation Database System Concepts - 6th Edition 2.23 Figure 2.04: The Instructor relation ©Silberschatz, Korth and Sudarshan Figure 2.06: The Section relation Figure 2.07: The Teaches relation Database System Concepts - 6th Edition 2.24 ©Silberschatz, Korth and Sudarshan Figure 2.13: selecting attributes ID and salary of instructors with salary greater than $85000 Figure 2.10: selecting instructors with salary greater than $85000 Figure 2.11: selecting ID and salary attributes from the instructor relations Figure 2.12: Natural Join of the instructor and department relations Database System Concepts - 6th Edition 2.25 ©Silberschatz, Korth and Sudarshan End of Chapter 2 Database System Concepts, 6th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use