Chapter 3 The Relational Database Model

Chapter 3 The Relational Database Model -...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 3 The Relational Database Model Tthe relational database model takes a logical view of data The relational model's basic components are entities, attributes, and relationships among entities How entities and their attributes are organized into tables About relational database operators, the data dictionary, and the system catalog How data redundancy is handled in the relational database model Why indexing is important A logical View of Data Relational model o Enables us to view data logically rather than physically o Reminds us of simpler file concept of data storage or spreadsheet concept of table Table o Two-dimensional structure composed of rows and columns o Has advantages of structural and data independence o Resembles a file from conceptual point of view o Easier to understand than its hierarchical and network database predecessors Tables Table also called a relation because the relational model's creator, Codd, used this term. A relation (and a relational DBMS's table) differs from a table in that there is no default order of rows or columns o Note SQL does use a column order but this is a limitation of SQL, not the model. Each row (tuple) represents a single entity in an entity set Each column represents an attribute and each must have a distinct name Each row/column intersection (cell) represents a single atomic value All values in a column must have same data format Each column has a specific range of values known as a domain Each row must have some combination of attributes that uniquely identifies it (key) Student Table Example
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Keys A key consists of one or more attributes that determine other attributes Primary key (PK) is an attribute (or a combination of attributes) that uniquely identifies any given entity (row) Key's role is based on determination o If you know the value of attribute A, you can look up (determine) the value of attribute B Types of Keys
Background image of page 2
Composite key Key consisting of multiple attributes
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 19

Chapter 3 The Relational Database Model -...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online