What is Microsoft Access

What is Microsoft Access made up of?

The Microsoft® Access Database is made up of 7 major components:

• Tables;
• Relationships;
• Queries;
• Forms;
• Reports;
• Macros;
• Modules.

 The following gives a quick overview of each component. 

Tables

The tables are the backbone and the storage container of the data entered into the database. If the tables are not set up correctly, with the correct relationships, then the database may be slow, give you the wrong results or not react the way you expect. So, take a bit of time when setting up your tables.

 Queries, forms, etc. are usually based on a table.

The tables that contain data look a bit like a table in Microsoft® Word or a Microsoft® Excel Spreadsheet, when opened.  They have columns and rows as does a table in Microsoft® Word and an Excel worksheet.  Each of the columns will have a field name at the top and each of the rows will represent a record.

 As an example: 

Relationships

Relationships are the bonds you build between the tables. They join tables that have associated elements.  To do this there is a field in each table, which is linked to each other, and have the same values.

Queries

Are the means of manipulating the data to display in a form or a report.  Queries can sort, calculate, group, filter, join tables, update data, delete data, etc.  Their power is immense.  The Microsoft® Access database query language is SQL (Structured Query Language).  The need to know SQL is not required in the early stages of learning Access. Microsoft® Access writes the SQL for you, after you tell it what you want, in the Design view of the queries window.

Forms

Forms are the primary interface through which the users of the database enter data.  The person who enters the data will interact with forms regularly. The programmer can set the forms to show only the data required. By using queries, properties, macros and VBA (Visual Basic for Applications), the ability to add, edit and delete data can also be set. Forms can be set up and developed to reflect the use they will be required for.

Reports

Reports are the results of the manipulation of the data you have entered into the database. Unlike forms, they cannot be edited.  Reports are intended to be used to output data to another device or application, i.e. printer, fax, Microsoft® Word or Microsoft® Excel.

Macros

Macros are an automatic way for Access to carry out a series of actions for the database.  Access gives you a selection of actions that are carried out in the order you enter.  Macros can open forms; run queries, change values of a field, run other Macros, etc. the list is almost endless.

Modules

Modules are the basis of the programming language that supports Microsoft® Access, The module window is where you can write and store Visual Basic for Applications (VBA).  Advanced users of Microsoft® Access tend to use VBA instead of Macros.

 All of the above components are persistent; this means that changes are saved when you move from one component to another, not when the database is closed, as in a Microsoft® Word Document.

Limitations

The total size of a database file (.MDB) is limited only by the storage capacity of your PC (Microsoft® quote the maximum database size of 2 Gigabyte (2000 Megabytes)). These figures are for pre 2007 versions of Microsoft Access.

Very few realistic limitations exist, though here are some parameters:

Maximum table size                                                   1 Gb

No. of fields in a record or table                                     255

No. of indexes in a table or record                                   32

No. of fields in an index                                                  10

No. of tables in a query                                                  32

Maximum size of a form or report                                   22"

Characters in a memo field                                       64,000

No. of characters in object names                                   64

.MDB size                         2 Gb (or storage capacity of PC)

Max integer                                                 2,147,483,648

Concurrent users                                                         255

Relational Database

Now that you understand a bit of what is Microsoft Access. it is time to explain what a relational database is. The relational database was invented by E. F. Codd at IBM in 1970.The power of a relational database is the ability to bring a lot of information together quickly. I am not going into too much technical detail of what a relational database but hope to explain it in simple terms, so it is possibly not 100% technically accurate.  To me these are the rules of a relational database:

• No duplicate data (except linked fields - explained shortly)
• Information is broken into categories
• Data is broken down to the smallest useable bit.  For example a persons name would be broken down into 4 sperate sections title, first name, middle name and last name.
• Each record has a unique identifier, this distinguishes a particular record from any other record

To explain this I will give an example below:

For the purpose of this example, we will be looking at a Library data base from a relational database viewpoint. For a Library database we would want to collect the following information:

• Information about the books;
• Information about the borrowers;
• Information about when a book was borrowed and by whom.

 You may be tempted to include all this information within the one table.  Once you start entering data the following occurs: 

Entering data this way requires multiple entries (and duplicate data in some of the columns)

This can lead to the following problems:

• Data entry errors (see bolded items);
• The user having to enter the same information over and over;
• The database would grow very big, very quickly, causing it to run slower.

Therefore, to meet the rules of a relational database we would first break this one large table into smaller tables of like information (categories). As an example:

• Table One (tblBook) would contain information about the books;
• Table Two (tblBorrower) would contain information about the borrowers; and
• Table Three (tblLoan) would contain information about the borrowing of a book.

The next step is to list all the facts you think are required for each of these tables underneath them.

I have included the examples below for each of the tables for the library database. The primary key and foreign key fields will be explained a bit later.

Note:  

¨       The fields have been broken down in to their smallest logical part.  As an example, a person’s name has been broken down to:

Surname;

First name;

Title.

¨       The information is only recorded once, i.e. we do not include all the information about the customer in the tblLoan table.

 Primary Key - Unique Identifier

An important part of determining the fields for each table is deciding which field (if any) is suitable as the primary key.

The power of a relational database is the ability to bring a lot of information together quickly. For this to work efficiently and effectively, Microsoft® Access needs to be able to identify unique records.  For this reason, one field or a set of fields needs to be unique.  This can be a unique identification number such as a Medicare number, Employee ID number, Pension number, etc.:  

• A primary key cannot contain duplicate values, e.g. a person’s last name is not suitable as a primary key as there is often more than one person with the same last name;

• A primary key cannot contain null values, therefore a field such as a phone number is not suitable, as you may not know the person’s phone number when you first enter them into the database;

• Also, if the information contained in the Primary Key is likely to be altered, then it is best to avoid this field as well.

If a unique identifier cannot be identified (which is more than likely), you can add a field, which will automatically increase sequentially by one, thus providing the record with a unique identifier.

Foreign Keys

The Foreign Key is the field that links a related table to the main table.  As an example, in the library database, a borrower may appear many times in the ‘Loan’ table, as a borrower may borrow many books.  A book may also occur many times in the ‘Loan’ table as a book can be borrowed many times.  Therefore, the loan table would contain many links to a particular borrower and many links to a particular book, but each loan record would relate to only one book and one borrower.  This is illustrated below:

• The ‘tblBorrower’ table is linked to the  ‘Loan’ table with the BorrowerID and BorrowerFK fields;

• The ‘Book’ table is linked to the ‘Loan’ table with BookID and BookFK fields.

These fields are known as foreign keys (FK). Note: that only the ID field is kept in the loan table, no other information is needed from the borrower table or the book table.  By setting up relationships between the tables, Microsoft Access knows which foreign key belongs to which primary key (unique identifier) and can pull the information from the relevant tables when needed.

If this does not quite cover what you are looking for then try:

What is Microsoft Access at Wikipedia.com

Most of this information on 'What is Microsoft Access' has been taken from my Tutorial on Microsoft Access.  If you would like a free copy then just fill in the form below.