Part 1: Par t Title
What Is Microsoft Access.
5
Pa rt 1: Understanding Microsoft Access
Some Relational Database Terminology
Rela tion Information about a single subject such as customers, orders, employees,
products, or companies. A relation is usually stored as a table in a relational data-
base management system.
Attribute A specific piece of information about a subject, such as the address for a
customer or the dollar amount of an order. An attribute is normally stored as a
data column, or field, in a table.
Instance A particular member of a relation—an individual customer or product. An
instance is usually stored in a table as a record, or row.
Relationship The way information in one relation is related to information in
another relation. For example, customers have a one-to-many relationship with
orders because one customer can place many orders, but any order belongs to
only one customer. Companies might have a many-to- many relatio nship with
contacts because there might be multiple contacts for a company, and a contact
might be associated with more than one company.
Join The process of linking tables or queries on tables via their related data values.
For example, custom ers m ig ht b e joined to ord ers by ma tch ing cust omer ID in a
customers table and an orders table.
Database Capabilities
An RDBMS gives you complete control over how you define your data, work with it, and
share it with others. The system also provides sophisticated features that make it easy to cat-
alog and manage large amounts of data in many tables. An RDBMS has three main types of
capabilities: data definition, data manipulation, and data control.
Data definition You can define what data is stored in your database, the type of data (for
example, numbers or characters), and how the data is related. In some cases, you can
also define how the data should be formatted and how it should be validated.
Data manipulation You can work with the data in many ways. You can select which data
fields you want, filter the data, and sort it. You can join data with related information
and summarize the data. You can select a set of information and ask the RDBMS to
update it, delete it, copy it to another table, or create a new table containing the data.
Data control You can define who is allowed to read, update, or insert data. In many cases,
you can also define how data can be shared and updated by multiple users.
All this functionality is contained in the powerful features of Microsoft Access. Let’s take a
look at how Access implements these capabilities and compare them to what you can do with
spreadsheet or word processing programs.
|
|