Transcript Introduction to Database

Introduction to Database
CSC 240 (Blum)
1
Data versus Information
• When people distinguish between data and
information,
– Data is simply a set of individual numbers or
facts.
– Information arises from integration – putting
the individual facts together to see the larger
picture or by asking a question not answerable
by just one piece of data.
CSC 240 (Blum)
2
Data vs. Information Example
• Example of Data:
– John Smith got a 87 on Test 2 in CSC 240.
• Examples of Information:
– John Smith scored more than 10 points over the
class average on all of the tests in CSC 240.
– Jane Jones got the highest score on Test 2 is
CSC 240.
CSC 240 (Blum)
3
Database
• The purpose of a database is to bring together a set
of data so that it is centralized, organized, easy to
extract information from, and so forth.
• The way the facts are organized and how they
relate to each other is known as the database
design.
• The software application that facilitates the storing
of the data and the accessing of the information is
known as a database management system.
CSC 240 (Blum)
4
Database Modeling
• In database design, one tries to organize the
data in a way that reflects the situation from
which the data comes.
• One approach is known as entityrelationship modeling or ER modeling.
• The design is often represented pictorially
in an ER Diagram.
CSC 240 (Blum)
5
Entities
• Entities separate the data into distinct units.
– E.g. a Person entity collects together individual pieces
of data (known as attributes) about a person – Name,
Address, PhoneNumber, etc.
• Database entities often reflect real objects/entities
(persons, buildings, courses, etc.)
• An entity is somewhat similar to an object in
programming, it collects data that belongs together
in some immediate way.
CSC 240 (Blum)
6
Relationship
• The various entities may be distinct, but
they are not completely disconnected. An
association between two entities is known
as a relationship.
– In a database modeling a university, one would
have relationships, such as
• Student takes class
• Professor teaches class
• Etc.
CSC 240 (Blum)
7
ER Diagram
• One can visualize the entities and their
relationship using an Entity-Relationship
(ER) diagram.
– The entities are represented by rectangles.
– The relationships are represented by arrows
between the rectangles.
• The arrow may include a verb to capture the nature
of the relationship (as well as other notations).
CSC 240 (Blum)
8
CSC 240 (Blum)
9
Design  Implementation
• After a database is designed, one uses a
database management system to
implement (actually make) the database.
• In database implementation, one encounters
terms like table, record, field, keys, and so
forth.
CSC 240 (Blum)
10
Webopedia definition of record
• “In database management
systems, a complete set of
information. Records are
composed of fields, each of
which contains one item of
information. A set of records
constitutes a file. For example, a
personnel file might contain
records that have three fields: a
name field, an address field, and
a phone number field. In
relational database management
systems, records are called
tuples.”
CSC 240 (Blum)
11
Whatis definition of table
• “In a relational database, a table (sometimes called a file)
organizes the information about a single topic into rows and
columns. For example, a database for a business would typically
contain a table for customer information, which would store
customers' account numbers, addresses, phone numbers, and so
on as a series of columns.
• Each single piece of data (such as the account number) is a field
in the table. A column consists of all the entries in a single field,
such as the telephone numbers of all the customers.
• Fields, in turn, are organized as records, which are complete
sets of information (such as the set of information about a
particular customer), each of which comprises a row. The
process of normalization determines how data will be most
effectively organized into tables.”
CSC 240 (Blum)
12
CSC 240 (Blum)
13
Fields
• The lower-level pieces of data gathered together to
form an entity are known as fields or attributes or
properties.
– Thus in our example the Person entity consists of fields
like FirstName, LastName, Address and PhoneNumber,
etc.
• Fields are analogous to properties of an object.
• Like properties, they have a type (Text, Number,
Yes/No, Memo, Date/Time, etc.) which indicate
how the information is to be stored and
interpreted.
CSC 240 (Blum)
14
Webopedia definition of the key
• “In database management systems, a key is a field
that you use to sort data. It can also be called a key
field, sort key, index, or key word. For example, if
you sort records by age, then the age field is a key.
• Most database management systems allow you to
have more than one key so that you can sort
records in different ways.
• One of the keys is designated the primary key, and
must hold a unique value for each record.
• A key field that identifies records in a different
table is called a foreign key.”
CSC 240 (Blum)
15
References
• Database Systems: Design, Implementation,
& Management, Peter Rob and Carlos
Coronel
• http://www.whatis.com
• http://www.webopedia.com
CSC 240 (Blum)
16