Courses/Computer Science/CPSC 203/CPSC 203 2007Fall L04/CPSC 203 2007Fall L04 Lectures/Lecture 10
The purpose of this lecture is to further introduce you to the relational database model in a visual fashion. We will focus on a triad of ideas:
- In A Database --- Everything is Abstacted to 2-D tables. ("It's Tables all the way down").
- A table represents is a set of values for some object -- identified by the Primary Key. Each row in a table specifies a set of attributes for an "instance" of an object (an individual).
- All operations in a database are operations on sets of values.
The objectives of today's class are:
- House Keeping
- Text Reading -- Chapter 11
- Assignment 1 Spreadsheet -- Cell AB34 should be a 0. Email appears twice -- as used in different contexts in the survey.
- Homework ' -- Try out Freebase. A free online database, available at: http://www.freebase.com/signin/\
- Glossary Review (including Relational DB Meta Model)
- Triad of Database Ideas.
- Final Idea -- In a database, the Primary Key identifies each member of a set.
- The Books Example Database.
- Set - A set is a collection of unique objects. In databases, everything is in sets and subsets of information. Sets, Subsets, Intersection sets and Union sets were introduced in class via "Venn Diagrams": http://en.wikipedia.org/wiki/Venn_diagram
- Table - A row (case) by column (variable) display. An entity that has a group of related records. In Relational Databases, a table if often called a "Relation". It is also called an "Entity".
- Parent: A Parent-Table or Entity has it's primary key linked to one to many foreign keys in the Child table.
- Child: A Child-Table or Entity has a foreign key(s) that link it back to one or more Parent Tables. The child tables foreign keys are primary keys in the parent tables.
- Query – A way of asking questions of a database. In general a query of a table(s) returns a subset of the table(s) for which the query parameters are true. For example, which people in the class listed Google as their most frequently visited website. More formally, a query is a proposition about data extracting a subset of information based on specific requirements using the primary and foreign keys. A query language is used to set up these requests and the query can be repeated at different times for updated information
- Domain – “Data Type” = accepted values and operations. A set of values of a specific type with allowable operations that can apply to many attributes. Every field or column must be assigned a data type which is a domain (with specific rules) such as:
- Attribute – a feature of an entity (object, variables)
- Entity – an object in the world, which can have many relationships with other entities
- Relationship – Intersection set of keys for 2 tables. A link between two entities.
- Join – the relations between entities or Parent Table (on primary key) and Child Table (on foreign key)
- One-to-One: Ex: a student can only borrow one book
- One-to-Many: Ex a student can take many courses
- Many-to-Many: Ex: many students can take many courses. Joins can break down into multiple One-to-Many joins.
- Key – a unique identifier: data value that makes the row of information completely different from any other row
- Primary: primary unique id of an instance (case)
- Foreign: key linked to Primary key of parent table
- Index - A look up table for a column with repeating values that makes queries on this column more efficient.
- Referential Integrity -- Put simply, the restriction that no entry in a child table can be made unless the foreign key for that entry matches an existing primary key in the parent table(s). See Wikipedia: http://en.wikipedia.org/wiki/Referential_Integrity
- Entity Relationship Diagram (ER-D) -- A diagramatic summary of the tables in a database and their relationships. We use a simple version of ER-D in this course -- for more information see http://en.wikipedia.org/wiki/Entity-relationship_diagram
- Cartesian Product Muliplying each element in one set by every element in another set. In Relational Databases, a cartesian product is the default result of including two tables in a query without a join. For those interested in the math side of this see, http://en.wikipedia.org/wiki/Cartesian_product
We will cover the following concepts, largely using visual models and a small 'Books' database example.
- The Relational Database Meta Model -- tells you 'what' a database is in the abstract. It is usually implemented as a set of tables. That is, there is an underlying database (from the meta-model) that keeps track of every specific database you build.
- More practice on thinking about relational databases in terms of sets.
- A first look at a very simple relational database on Books.
TIA 3rd Edn: Chapter 11. 462 -- 503
TIA 4th Edn: Chapter 11. pp 484 -- 525
E.F. Codd's original proposal for the Relational Data Model can be found online at: http://www.cs.nott.ac.uk/~nza/G51DBS/codd.pdf "A Relational Model of Data For Large Shared Data Banks" created the theory behind the modern databases used in large organizations today. While technical -- the introductory parts of the article are accessible to the general lay reader and provide a good introduction to the thinking style needed to "Grok" databases.
- The Database Relational Model. A Retrospective Review and Analysis. 2001. By C.J. Date
- Practical Issue in Database Management -- A Reference for the thinking Practioner.2000. By Fabian Pascal
- The Essence of SQL. A Guide to Learning the Most SQL in the Least Amount of Time. 1996. By David Rozenshtein
- SQL Visual Quickstart Guide. 2005. By Chris Fehily.