I.
Terminology
II.
Database Technology
III. The Architecture of a Database
Management System (DBMS)
IV. The Database Administrator

A. Field
B. Data Occurrences
C. Fixed vs. Variable Length Records
D. Record Key
E. Sort Keys

A field is the smallest block of data that will be stored and retrieved in the information system.
Other names for field include data item, attribute, or element.
Field 1 Field 2

A specific set of data values for a record in a file.
3
4
1
2
5
The above table contains 5 occurrences of account records for the general ledger account file.

Fixed Length Records

Both the number of fields and the length of each field are fixed.

Strength: Easier to manipulate records.

Weakness: Must accommodate maximum sizes.
Variable Length Records

Both the number of fields and the length of each field are variable. (See Fig. 15-1 on p. 603)

Strength: Less waste of memory when maximum sizes do not have to be accomodated.

Weakness: Record manipulation is more difficult.

1110
1500
2105
2110
A record key is a field or combination of fields that uniquely identifies a particular record in a file.


Primary sort key – The first field used to sort the data occurrences in a record set.

Secondary sort key – A field used to determine relative position among a set of data occurrences in a record set.

Tertiary sort key – Additional fields beyond primary and secondary sort keys that are required to uniquely identify data occurrences in a record set.
Last Name First Name
Adams Tom
Jones
Jones
Jones
Alisa
Julie
Julie
Young Sam
Age
25
36
19
21
22

A. The Problem of Redundancy
B. The Components of a Database

That is not what we show per our records.

Redundancy occurs when different areas of an organization use the information system to store the same information in more than one place.

Results in update anomaly.

1. Data Description Language (DDL)
2. Data Manipulation Language (DML)
3. Data Query Language (DQL)

Defines the logical structure of the database (known as the schema). Defines the following:

Name of data fields.

Type of data (numeric, alphabetic, etc.)

Number of positions
(length of field).

May also define subschema (i.e., individual user views)

Pull a trial balance.

The DML consists of the commands for updating, editing, manipulating, and extracting data.

Structured query language
(SQL) is a common DML in relational settings.
Structure Query Language (SQL)

A data query language is a user friendly language or interface that allows the user to request information by simply filling in blanks. Represents a special type of
DML.

III. The Architecture of a Database
Management System (DBMS)
A. The Database Architecture
B. The Conceptual Architecture and Entity-
Relationship (ER) Diagrams
C. Logical Data Structures
D. The Physical Structure

Conceptual
Level
Logical Level
Physical Level
Database contents
Uses of database
Desired reports
Information to be viewed
Logical data structures:
Tree
Network
Relational
Access Methods:
Sequential Access
Indexed Files

B. The Conceptual Architecture and Entity-
Relationship (ER) Diagrams
PART_NO NAME
PART
STORED AT
COST

Square boxes are used for entities
(separate tables).

Ellipses are used for attributes (table columns).

Diamond shaped boxes depict relationships.
LOCATION
WHSE ADDRESS

1. Tree or Hierarchical Structure
2. Network Structures
3. Relational Structure a. Selection b. Projection c. Join

1. Tree or Hierarchical Structure
A parent record can have many children. However a child record can have only one parent.
Can only model 1:1 (one-to-one) and 1:* (one-to-many) relationships.
Commonly used with accounting data. Can only access data by going from a parent to child.
Assets
Current Assets
Long-term Assets
Balance Sheet
Liabilities
Current Liabilities
Long-term Liabilities
Equity
Revenues
Expenses

Eliminates the distinction of parent and child records. A parent can have many children and a child can have many parents.
Can model 1:1 (one-to-one), 1:* (one-to-many), and *:* (many-to-many) relationships.
Must know the physical structure of the data in order to access it.


Relational databases organize and store data in two dimensional tables consisting of rows and columns.

Relationships among tables are represented by common data values in different tables.

Straight forward in terms of organizing and searching the data.

Possesses ad hoc search capabilities.

Produces a horizontal subset (includes entire row) of a relation which satisfies a boolean predicate.
Savings Table
Name
John
Bill
Mary
Joe
Acct #
123
205
707
127
Balance
35.75
3.95
7.95
4.05
(Savings)
Balance < 5.00
Bill
Joe
Name Acct #
205
127
Balance
3.95
4.05

Constructs a vertical subset of a relation. The subset is obtained by selecting specified attributes and removing others.
Savings Table
Name
John
Bill
Mary
Joe
Acct #
123
205
707
127
Balance
35.75
3.95
7.95
4.05
(Savings)
Name Balance < 5.00
Name
Bill
Joe

3c. Join
A join is used to combine 2 tables. The attribute used to join must be in both tables.
Table R
A B C
C
Table S
D E a1 b1 c1 c2 d1 e1 a2 b2 c2 c3 d2 e3 a2 b2 c3 c2 d1 e2 a4 b2 c2
R |X| S
A a2 a2 a2 a4 a4
B b2 b2 b2 b2 b2
C c2 c2 c3 c2 c2
D d1 d1 d2 d1 d1
E e1 e2 e3 e1 e2

1. Sequential Access
2. Indexed Files

 Records can only be accessed in a predefined sequence. For example, if there are 100 records in a file, one must access the first 99 records before accessing the last record.

Generally useful for batch processing when nearly all records must be accessed.


Any attribute can be extracted from the records in a primary file and used to build a new file whose purpose is to provide an index to the original file.

First, the index is searched to find a specified value of an attribute such as an customer account number.

Second, the disk addresses are used to directly retrieve the desired records

See Fig. 12-13 on p. 427.

This is not quite what we need.
The database administrator is a person who coordinates data management activities such as approving the physical contents and user views of the database.


Fields and keys

Three Components of a DBMS

Three Types of Database Architecture

The Database Administrator