Databases

A database is a data set with a regular structure.

Its front-end allows data access, searching and sorting routines.

Its back-end affords data inputting and updating. A database is usually but not necessarily stored in some machine-readable format accessed by a computer. There are a wide variety of databases, from simple tables stored in a single file (or even on sheets of paper),  to modern very large databases with many millions of records, stored in rooms full of disk drives or other peripheral electronic storage devices. 

In software design, the front-end is the part of a software system that deals with the user, and the back-end is the part that processes the input from the front-end.

•     Database Applications:

–    Banking: all transactions

–    Airlines: reservations, schedules

–    Universities:  registration, grades

–    Sales: customers, products, purchases

–    Manufacturing: production, inventory, orders, supply chain

–    Human resources:  employee records, salaries, tax deductions

Geographic systems, etc. ….

History of Databases development.

•   Punched cards (Hollerith) used at the beginning of the 20th century to record census data with mechanical machines to process the cards and tabulate the results.
• 1950s and early 1960s: magnetic tapes developed for data storage and used in conjunction with punched cards to update a master file onto a new tape. All sequential processing with sorted files
• Late 1960s and 1970s: widespread use of hard disks; direct access to data. Freed from sequential processing, databases could be created to store data on disk.      Codd E.F.  publishes paper on relational databases  
•      1980s: Relational model not used in practice at first because of performance problems. IBM developed System R, a relational database with much more efficiency. Hierarchical and network databases replaced and SQL takes off 
•   Early 1990s: Decision support and querying re-emerged as a major application area; data warehousing and data mining grow as well
•     Late 1990s: WWW is a catalyst for the deployment of databases with very high transaction rates, and very high reliability

System

“A system may be defined as a set of connected parts united by some form for regular interaction or interdependencies”.

Information Systems

Information systems exist in all organizations and range in complexity :

Managerial and Technical

Formal or informal.

Manual,  Mechanized,  Computerized.

Fields of CS closely connected with Databases Theory and Applications:

MIS and DSS(Management Information s. & Decision Support Systems)

DSS and effective planning  and effective control.

DSS and Artificial intelligence:

Expert Systems (ES), Data Mining

Intelligent maintenance and safety diagnostics.

The Internet.

 Database Management System (DBMS) :

-A software package/system to facilitate the creation and maintenance of a computerized database.

-Set of programs to access the data and to protect the database against hardware or software crashes and against unauthorized access.  

DBMS provides an environment that is both convenient and efficient to use.   One of main Functions of DBMS  is the shielding of database users from the hardware-level details.

 Other of main functions of DBMS is persistent storage of data and data structures (i.e. for long period, compatibility with different programming languages and software, e.g. 75 yrs. in banks because inheritance problem).

Database System (DBS):

 The DBMS software together with the data itself. Sometimes, the applications are also included.

A database system is essentially nothing more than a computerized record-keeping system. The DBS itself can be regarded as a kind of electronic filing cabinet or a repository for a collection of computerized data files with collection of interrelated data. DBS contains information about a particular enterprise

Meta-Data

Meta-data is data about data 

Metadata is stored in special catalog (DBMS) which contains information such as structure each data file, and it describes the structure of database.

Metadata helps you understand what information you have, where it is located, and what value it provides to users. Users can view information in a context they understand, providing a more efficient and intuitive way to communicate

The relation between meta-data, model and data is that meta-data enable user/application to search for certain data in an efficient manner. It is “ROAD MAP” for model to locate data.

Typical examples of meta-data are lists, catalogues and search systems in library (Why?).

(e.g. m-d. and .dbf files – header of files contains info about structure of DB)

 

Characteristics of DBS:

-Self-describing nature. DBS contains DB as well as complete definition and description of DB structure and constraints (MD-DB).

(e.g. .dbf files – as example of RDB, copy structure extended)

-Insulation between prg, data, and data abstraction.

(e.g. application softw. may independents of DB modifying, insert, change etc.)

- Support of multiple views of the data, and control of security multi-user transaction processing.

(select, passwords, concurrency control,…)

USER

•     Users are differentiated by the way they expect to interact with the system

•     Application programmers – interact with system through DML calls,

write specialized database applications that do not fit into the traditional data processing framework

•     End user :

- Naïve users – invoke one of the permanent application programs that have been written previously, e.g. people accessing database over the web, bank tellers, clerical staff

 - Sophisticated users – form requests in a database query language

 - Specialized users – write specialized database applications that do not fit into the traditional data processing framework

System Analyst, Database Designer :   mediator, middleman between end users and programmers during software development project.

(Especially at stages of requirement analysis and design, and implementation,…)

DATABASE SYSTEM ADMINISTRATOR (vip!)

•      Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs.

•     Database administrator's duties include:

–    Schema definition

–    Storage structure and access method definition

–    Schema and physical organization modification

–    Granting user authority to access the database

–    Specifying integrity constraints

–    Acting as liaison with users

–    Routine maintenance

•     Backups

•     Upgrades

•     Monitoring performance and responding to changes in requirements