CHAPTER 12 - DATABASES

                   SUMMARY CHAPTER 12

DATA

• Data consists of facts or observations about people, places, things, and events. 
• Not long ago, data was limited to numbers, letters, and symbols. 
• Now data includes : 

1. Audio - captured, interpreted and saved using microphones and voice recognition systems. 
2. Music - download from the Internet and captured from others sources, rearranged, and used to create customized CDs. 
3. Photographs - captured by digital cameras, edited by image-editing software, and shared with others over the Internet. 
4. Video - captured by digital video cameras and TV tuner cards, saved, and used in presentations. 

• There are two ways or perspectives to view data : 

1. Physical view - focuses on actual format and location of data, very specialized computer professionals are concerned with this view. 
2. Logical view - focuses on meaning and content of data, end users and most computer professionals are concerned with this view. 

• This chapter presents the logical view of data and how data is stored in databases. 

DATA ORGANIZATION

• is organized by the following groups :

1. Character - the most basic logical elements, consisting of individual numbers, letters, and special characters. 
2. Field - the next level consisting of a set of related characters. Example a person's last name. A data field represents an attribute (description or characteristic) of some entity (person, place, thing, or object). 
3. Record - a collection of related fields. Example, a payroll record consisting of fields of data relating to one employee. 
4. Table - a collection of related records. Example, a payroll table consisting of all the employee records. 
5. Database - an integrated collection of related tables. Example, a personnel database contains all related employee table, including the payroll and the benefits tables. 

Key Field

• also known as the primary key. 
• is the field in a record that uniquely identifies each record. 
• Tables can be related to other tables by key fields.
• Key fields in different files can be used to integrated the data in a database. 
• Common key fields are employee ID numbers and driver's license numbers. 
• Example, in the Personnel Database, both the Payroll and the Benefits tables include the fields Employee ID. 

Batch versus Real-Time Processing

• Traditionally, data is processed in one of two ways. 
• These are batch processing, or what we might call "later", and real-time processing, or what we might call "now". 
• Two methods have been used to handle common record-keeping activities such as payroll and sales orders.

1. Batch processing - data is collected over time and then processed later all at one time (batched). Example, monthly credit card bills are typically created by processing credit card purchases throughout the past month.
2. Real-time processing (online processing) - data is processed at the same time the transaction occurs, direct access storage devices make real-time processing possible. Example, a request for cash using an ATM machine initiates a verification of funds, approval or disapproval, disbursement of cash, and an update of the account balance. 

DATABASES

• is a collection of integrated data logically related files and records. 
• Example, records for the same customer may appear in different files in the sales department, billing department, and credit department, this is called data redundancy. 
• Example, a product ordered might be sent to the new address, nut the bill might be sent to the old address, this situation result from the lack of data integrity. 

Need For Databases

• Advantages of databases are : 

1. sharing data 
2. improved security
3. reduced data redundancy
4. higher data integrity 

Database Management

• A database management systems (DBMS) is the software for creating, modifying, and gaining access to the database. 
• A DBMS consists of five subsystems : 

1. DBMS Engine - provides a bridge between logical and physical data view. 
2. Data definition subsystem - defines the logical structure of a database using a data dictionary or schema. 
3. Data manipulation subsystem - provides tools for data maintenance and data analysis, tools include query-by-example and structure query language (SQL). 
4. Application generation subsystem - provides tools for creating data entry forms with specialized programming languages. 
5. Data administration subsystem - manages the database, database administrators (DBAs) are computer professionals who help define processing rights. 

DBMS STRUCTURE

• DBMS programs are designed to work with specific data structure or database models. 
• These models define rules and standards for all the data in the database.
• Five principals database models are :

1) Hierarchical Database 

• uses nodes to link and structure fields and records; entries may have one parent node with several child nodes in a one-to-many relationship. 

2) Network Database

• is like hierarchical except a child node may have more than one parent in a many-to-many relationship; additional connections are called pointers between parent nodes and child nodes. 
• Thus, a node may be reached through more than one path.
• It may be traced down through different branches. 

3) Relational Database 

• data is stored in tables (relations); related tables must have a common data item (key field). 
• A table and its data is called a relation. 
• Common data  item enabling information stored in one table to be linked with information stored in another. 

4) Multidimensional Database

• extend two-dimensional relational tables to three or more dimensions, sometimes called a data cube.
• Multidimensional Database offer more flexible structures than relational databases, providing a more intuitive means of modeling data. 
• Two of the most significant advantages are conceptualization and processing speed. 

5) Object-Oriented Database

• stores data, instructions, and unstructured data. 
• Data is organized using classes, objects, attributes, and methods.
• Classes are general definitions
• Objects are specific instances of a class that can contain both data and instructions to manipulate the data. 
• Attributes are the data fields an objects possesses. 
• Methods are instructions for retrieving or manipulating attribute values. 

TYPES OF DATABASES

• There are four types of databases : 

1) Individual 

• Individual database or microcomputer database is used by one person.
• It is a collection of integrated files primarily used by just one person. 
• Typically, the data and the DBMS are under the direct control of the user. 

2) Company

• Company databases are usually stored on a central server and accessed by multiple people.
• These databases are typically used for company operations. 

3) Distributed

• Distributed database is spread out geographically ; not all data is physical located in one place ; it is accessible by communications links. 
• Typically, database servers on a client/server network provide the link between the data. 

4) Commercial

• Commercial databases are generally enormous and cover particular subjects ; also known as information utilities and data banks. 
• Some important commercial databases are CSi , Dialog Information Services , Dow Jones Interactive Publishing , and LexisNexis. 
• Most of the commercial databases are designed for organizational as well as individual use. 

Citation : 

• COMPUTING ESSENTIALS COMPLETE 2010