Access is a database program that enables one can store
information such as a client list, products, invoices, inventory,
events, and other collections of data. In addition to entering the
data in a database table, you have several tools for working with
the data. Forms for simpler data entry can be created. You can
create a query to display a set of record. All these elements are
Access objects and are stored together in the database.
Microsoft Access is a powerful program to create and manage
your databases. In Access terms, a database is a collection of all
the tables, queries, forms, data access pages, reports, macros, and
modules that compose a complete system. Relational refers to the
fact that the tables that comprise the database relate to one
another.
4. Hierarchy that Microsoft Access uses in breaking down a
database
Database File
This is your main file that encompasses the entire database and
that is saved to your hard-drive or floppy disk. Example
StudentDatabase.mdb
Table
A table is a collection of data about a specific topic. There
can be multiple tables in a database. Example #1) Students Example
#2) Teachers
Field
Fields are the different categories within a Table. Tables
usually contain multiple fields. Example #1) Student LastName
Example #2) Student FirstName
Datatypes
Datatypes are the properties of each field. A field only has 1
datatype.
Database File Table Field Datatype Value
5. Opening/Creating an Existing Database
After starting Access, create a new database or open an
existing database. A database is stored as a file on your computer
or on a network computer. To work with the objects in a database,
one must open the database file. To open an existing database ,
follow these steps:
When Microsoft Access first starts up, a dialog box is
automatically displayed with options to create a new database or
open an existing one. If this dialog box is displayed, click Access
Database Wizards, pages, and projects and then click OK.
On the Databases tab, double-click the icon for the kind of
database you want to create.
Specify a name and location for the database.
Click Create to start defining your new database
6. Creating Tables in Database
A table is a collection of data about a specific topic, such as
students or contacts. Using a separate table for each topic means
that you store that data only once, which makes your database more
efficient, and reduces data-entry errors. Tables organize data into
columns (called fields) and rows (called records).
Primary Key
One or more fields (columns) whose value or values uniquely
identify each record in a table. A primary key does not allow Null
values and must always have a unique value. A primary key is used
to relate a table to foreign keys in other tables. For Example.,
make the Soc Sec # field the primary key, meaning that every
student has a social security number and no 2 are the same. To do
this, simply select the Soc Sec # field and select the primary key
button
7. Defining Relationships
After setting up multiple tables in your Microsoft Access
database, we need a way of telling Access how to bring that
information back together again. The first step in this process is
to define relationships between your tables. After this, one can
create queries, forms, and reports to display information from
several tables at once. A relationship works by matching data in
key fields - usually a field with the same name in both tables. In
most cases, these matching fields are the primary key from one
table, which provides a unique identifier for each record, and a
foreign key in the other table. For example, teachers can be
associated with the students they're responsible for by creating a
relationship between the teacher's table and the student's table
using the Teacher ID fields.
8. Steps for defining references
In the database window view, at the top, click on Tools --->
Relationships
Select the Tables you want to link together, by clicking on
them and selecting the Add Button
Drag the primary key of the Parent table (Teacher in this
case), and drop it into the same field in the Child table (Student
in this case)
Select Enforce Referential Integrity
When the Cascade Update Related Fields check box is set,
changing a primary key value in the primary table automatically
updates the matching value in all related records.
When the Cascade Delete Related Records check box is set,
deleting a record in the primary table deletes any related records
in the related table
Click Create and Save the Relationship
9. Creating a Form
It is a good idea to create a form using the wizard, unless you
are an advanced user and know what you are doing. Microsoft Access
does a very good job of creating a form using the wizard. The
following steps are needed to create a basic form:
Switch to the Database Window. You can do this by pressing F11
on the keyboard.
Click on the Forms button under Objects on the left side of
screen
Double click on Create Form Using Wizard
On the next screen select the fields you want to view on your
form.Click Next
Select the layout you wish
Click Next
Select the style you desire. Click Next
Give you form a name, and select Open the Form and enter
information
Select Finish
You should see your form. To adjust the design of your form,
simply hit the design button (same as with the tables), and adjust
your form accordingly
10. Creating a Report
A report is an effective way to present your data in a printed
format. Because you have control over the size and appearance of
everything on a report, you can display the information the way you
want to see it. If forms are for input, then reports are for
output. Anything you plan to print deserves a report, whether it is
a list of names and addresses, a financial summary for a period, or
a set of mailing labels. Again the Access Wizards walk you through
the process of defining reports.
Switch to the Database Window. You can do this by pressing F11
on the keyboard.
Click on the Reports button under Objects on the left side of
screen
Double click on Create Report Using Wizard
On the next screen select the fields you want to view on your
form. Most of the time you would select all of them.
Click Next
Select if you would like to group your files. Keep repeating
this step for as many groupings as you would like.
Click Next
Select the layout and the paper orientation you desire. Click
Next
Select the style you desire..Click Next
Give you report a name, and select Preview the Report
Select Finish
11. Difference between File processing & DBMS
A number of characteristics distinguish the database approach
from the traditional approach of programming with files. In
traditional file processing, each user defines and implements the
files needed for a specific application as part of programming the
application. For example, one user, the grade reporting office, may
keep a file on students and their grades. Programs to print a
students transcript and to enter new grades into the file are
implemented. A second user, the accounting office, may keep track
of students fees and their payments. Although both users are
interested in data about students, each user maintains separate
filesand programs to manipulate these filesbecause each requires
some data not available from the other users files. This redundancy
in defining and storing data results in wasted storage space and in
redundant efforts to maintain common data up-to-date. In the
database approach, a single repository of data is maintained that
is defined once and then is accessed by various users. The main
characteristics of the database approach versus the file-processing
approach are the following.
12. Characteristics of DBMS
Self-Describing Nature of a Database System-
A fundamental characteristic of the database approach is that
the database system contains not only the database itself but also
a complete definition or description of the database structure and
constraints. This definition is stored in the system catalog, which
contains information such as the structure of each file, the type
and storage format of each data item, and various constraints on
the data. The information stored in the catalog is called
meta-data, and it describes the structure of the primary database.
The catalog is used by the DBMS software and also by database users
who need information about the database structure. A general
purpose DBMS software package is not written for a specific
database application, and hence it must refer to the catalog to
know the structure of the files in a specific database, such as the
type and format of data it will access. The DBMS software must work
equally well with any number of database applicationsfor example, a
university database, a banking database, or a company databaseas
long as the database definition is stored in the catalog.
Insulation between Programs & Data and Data
Abstraction
In traditional file processing, the structure of data files is
embedded in the access programs, so any changes to the structure of
a file may require changing all programs that access this file. By
contrast, DBMS access programs do not require such changes in most
cases. The structure of data files is stored in the DBMS catalog
separately from the access programs. We call this property
program-data independence. In object-oriented and object-relational
databases, users can define operations on data as part of the
database definitions. An operation (also called a function) is
specified in two parts. The interface (or signature) of an
operation includes the operation name and the data types of its
arguments. The implementation (or method) of the operation is
specified separately and can be changed without affecting the
interface. User application programs can operate on the data by
invoking these operations through their names and arguments,
regardless of how the operations are implemented. This may be
termed program-operation independence. The characteristic that
allows program-data independence and program-operation independence
is called data abstraction.
13. Characteristics of DBMS
Support of Multiple Views of the Data
A database typically has many users, each of whom may require a
different perspective or view of the database. A view may be a
subset of the database or it may contain virtual data that is
derived from the database files but is not explicitly stored. Some
users may not need to be aware of whether the data they refer to is
stored or derived. A multi-user DBMS whose users have a variety of
applications must provide facilities for defining multiple
views.
Sharing of Data and Multi user Transaction Processing
A multi user DBMS, as its name implies, must allow multiple
users to access the database at the same time. This is essential if
data for multiple applications is to be integrated and maintained
in a single database. The DBMS must include concurrency control
software to ensure that several users trying to update the same
data do so in a controlled manner so that the result of the updates
is correct. For example, when several reservation clerks try to
assign a seat on an airline flight, the DBMS should ensure that
each seat can be accessed by only one clerk at a time for
assignment to a passenger. These types of applications are
generally called on-line transaction processing (OLTP)
applications.
14. Types of end users
End users are the people whose jobs require access to the
database for querying, updating, and generating reports; the
database primarily exists for their use. There are several
categories of end users:
Casual end users - occasionally access the database, but they
may need different information each time. They use a sophisticated
database query language to specify their requests and are typically
middle- or high-level managers or other occasional browsers.
Naive or parametric end users make up a sizable portion of
database end users. Their main job function revolves around
constantly querying and updating the database, using standard types
of queries and updatescalled canned transactionsthat have been
carefully programmed and tested. The tasks that such users perform
are varied:
Bank tellers check account balances and post withdrawals and
deposits.
Reservation clerks for airlines, hotels, and car rental
companies check availability for a given request and make
reservations.
Sophisticated end users - include engineers, scientists,
business analysts, and others who thoroughly familiarize themselves
with the facilities of the DBMS so as to implement their
applications to meet their complex requirements.
Stand-alone users - maintain personal databases by using
ready-made program packages that provide easy-to-use menu- or
graphics-based interfaces. An example is the user of a tax package
that stores a variety of personal financial data for tax
purposes.
15. Advantages of using DBMS
Controlling Redundancy
In traditional software development utilizing file processing,
every user group maintains its own files for handling its
data-processing applications. For example, consider the UNIVERSITY
database; here, two groups of users might be the course
registration personnel and the accounting office. In the
traditional approach, each group independently keeps files on
students. The accounting office also keeps data on registration and
related billing information, whereas the registration office keeps
track of student courses and grades. Much of the data is stored
twice: once in the files of each user group. Additional user groups
may further duplicate some or all of the same data in their own
files. This redundancy in storing the same data multiple times
leads to several problems. First, there is the need to perform a
single logical updatesuch as entering data on a new studentmultiple
times: once for each file where student data is recorded. This
leads to duplication of effort. Second, storage space is wasted
when the same data is stored repeatedly, and this problem may be
serious for large databases. Third, files that represent the same
data may become inconsistent. This may happen because an update is
applied to some of the files but not to others.
Restricting Unauthorized Access-
When multiple users share a database, it is likely that some
users will not be authorized to access all information in the
database. For example, financial data is often considered
confidential, and hence only authorized persons are allowed to
access such data. In addition, some users may be permitted only to
retrieve data, whereas others are allowed both to retrieve and to
update. Hence, the type of access operationretrieval or updatemust
also be controlled. Typically, users or user groups are given
account numbers protected by passwords, which they can use to gain
access to the database. A DBMS should provide a security and
authorization subsystem, which the DBA uses to create accounts and
to specify account restrictions. The DBMS should then enforce these
restrictions automatically. Notice that we can apply similar
controls to the DBMS software.
16. Data Models & Schemas
One fundamental characteristic of the database approach is that
it provides some level of data abstraction by hiding details of
data storage that are not needed by most database users. A data
model is a collection of concepts that can be used to describe the
structure of a database and provides the necessary means to achieve
this abstraction. By structure of a database we mean the data
types, relationships, and constraints that should hold on the data.
Most data models also include a set of basic operations for
specifying retrievals and updates on the database. In addition to
the basic operations provided by the data model, it is becoming
more common to include concepts in the data model to specify the
dynamic aspect or behavior of a database application. This allows
the database designer to specify a set of valid user-defined
operations that are allowed on the database objects.
17. Categories of Data Models
Many data models have been proposed, and we can categorize them
according to the types of concepts they use to describe the
database structure.
High-level or conceptual data models- provide concepts that are
close to the way many users perceive data.
Low-level or physical data models- provide concepts that
describe the details of how data is stored in the computer.
Concepts provided by low-level data models are generally meant
for computer specialists, not for typical end users. Between these
two extremes is a class of representational (or implementation)
data models, which provide concepts that may be understood by end
users but that are not too far removed from the way data is
organized within the computer. Representational data models hide
some details of data storage but can be implemented on a computer
system in a direct way.
18. Definition of entity, attribute and relation
An entity represents a real-world object or concept, such as an
employee or a project, that is described in the database.
An attribute represents some property of interest that further
describes an entity, such as the employees name or salary.
A relationship among two or more entities represents an
interaction among the entities; for example, a works-on
relationship between an employee and a project
19. DBMS Architecture
Three important characteristics of the database approach,
are
Insulation of programs and data (program-data and
program-operation independence);
Support of multiple user views; and
Use of a catalog to store the database description (schema). In
this section we specify an architecture for database systems,
called the
The three-schema architecture, which was proposed to help
achieve and visualize these characteristics.
20. Levels of DBMS
The Internal or Physical Level
The collection of files permanently stored on secondary storage
devices is known as the physical database. The physical or internal
level is the one closest to physical storage, and it provides a
low-level description of the physical database, and an interface
between the operating system's file system and the record
structures used in higher levels of abstraction. It is at this
level that record types and methods of storage are defined, as well
as how stored fields are represented, what physical sequence the
stored records are in, and what other physical structures
exist.
21. Levels of DBMS
The Conceptual Level
The conceptual level presents a logical view of the entire
database as a unified whole, which allows you to bring all the data
in the database together and see it in a consistent manner. The
first stage in the design of a database is to define the conceptual
view, and a DBMS provides a data definition language for this
purpose. It is the conceptual level that allows a DBMS to provide
data independence. The data definition language used to create the
conceptual level must not specify any physical storage
considerations that should be handled by the physical level. It
should not provide any storage or access details, but should define
the information content only.
22. Levels of DBMS
The External or View Level
The external or view level provides a window on the conceptual
view which allows the user to see only the data of interest to
them. The user can be either an application program or an end user.
Any number of external schema can be defined and they can overlap
each other. Because they have responsibilities for the design and
maintenance for the design and maintenance of the database, they at
times need to be able to see the entire database. The external and
the conceptual view are functionally equivalent for these two
users.
23. Data Independence
The three-schema architecture can be used to explain the
concept of data independence, which can be defined as the capacity
to change the schema at one level of a database system without
having to change the schema at the next higher level. 2 types of
data independence:
Logical data independence is the capacity to change the
conceptual schema without having to change external schemas or
application programs. We may change the conceptual schema to expand
the database, or to reduce the database. In the latter case,
external schemas that refer only to the remaining data should not
be affected. Only the view definition and the mappings need be
changed in a DBMS that supports logical data independence.
Application programs that reference the external schema constructs
must work as before, after the conceptual schema undergoes a
logical reorganization. Changes to constraints can be applied also
to the conceptual schema without affecting the external schemas or
application programs.
Physical data independence is the capacity to change the
internal schema without having to change the conceptual (or
external) schemas. Changes to the internal schema may be needed
because some physical files had to be reorganizedfor example, by
creating additional access structuresto improve the performance of
retrieval or update. If the same data as before remains in the
database, we should not have to change the conceptual schema. For
example, providing an access path to improve retrieval of SECTION
records by Semester and Year should not require a query such as
"list all sections offered in fall 1998" to be changed, although
the query would be executed more efficiently by the DBMS by
utilizing the new access path.
