# relnl - Lecture 3 INFS614 INFS614, GMU 1 Homework: HW 1a is...

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INFS614, GMU 1 Lecture 3 INFS614

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INFS614, GMU 2 Homework: HW 1a is due today we will go over a solution after the break which will help you with HW 1b HW 1b is due next week HW 2 will be assigned next week For next week: read sections 4.1 and 4.2 (relational algrebra) brush up on your Greek letters! also: read wikipedia article on the “deep web”
INFS614, GMU 3 The Relational Model is (yet another) data model This one is based on rigorous set theory instead of abstractions like “entity” and “relationships” As a (full) data model it has: Data Structures : Relations (or Tables) Operations : Relational Algebra, Relational Calculus, SQL. Integrity Constraints : key uniqueness, referential integrity, etc. The Relational Model is the most widely implemented data model for databases today. Vendors: IBM DB2, Oracle, Microsoft SQL Server, . .. Open source: MySQL, PostgreSQL, . ..

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INFS614, GMU 4 Bigger context: requirements, conceptual design, schema design , physical design/tuning Our design+implementation focus in this course: Step 1: ER design (Conceptual design) Step 2: Translate into a Relational Schema (Schema design) Step 3: Insert data and query over the relational model (impacts tuning) Part 2 of this lecture
INFS614, GMU 5 Relation: has 2 parts: Schema + Instance Part 1: Schema (or “intension”) a template or description for the instance the schema includes: a relation name + a set of (attribute name:domain) pairs e.g.: Students( sid :string, name :string, login :string, age :integer, gpa :real) this specifies: the name of the relation (Students) a set of its attributes (e.g., sid) a domain for each attribute (e.g., string).

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INFS614, GMU 6 Part 2: Instance (or “extension”) – A relation instance (or simply “a relation”) is a set of unique rows The contents of the relation at a given moment in time. # of attributes = degree / arity degree is fixed by the schema note: schema evolution is a hard problem in practice! #of rows = cardinality the cardinality changes as rows are inserted or deleted. note: row order does not matter! a relation instance is a set, and sets are unordered
INFS614, GMU 7 sid name login age gpa 53666 Jones [email protected] 18 3.4 53688 Smith [email protected] 18 3.2 53650 Smith [email protected] 19 3.8 Instance S1 of Students() scheme Degree = 5 Cardinality =3; all rows distinct

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INFS614, GMU 8 Employees Schema: Employees ( ssn :integer, name :string, rank :integer, salary :float) An instance E1 of Employees : ssn name rank salary 633909767 Richard Boon A 75689.09 674627883 Adolfo Laurenti B 67890.00 193838904 Will Smith C 50000.00 534559257 Phil Collins B 68901.00 123456789 Brad Johnson D 45000.00 354681756 Martha Stewart D 53500.00 123223665 Ralph Ramagashi B 69886.00 231896598 Michael Jordan A 80999.00
INFS614, GMU 9

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INFS614, GMU 10 Based on set theory: – “A subset of the cartesian product of a set of domains” – Which domains?
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## This note was uploaded on 10/18/2009 for the course INFS 614 taught by Professor Staff during the Fall '08 term at George Mason.

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relnl - Lecture 3 INFS614 INFS614, GMU 1 Homework: HW 1a is...

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