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Overview of Database Systems
What is a Database? What are they used for?
A database is a collection of data that is stored for a specific purpose and organized in a manner that allows its contents to be easily accessed, managed, and updated. Although this definition includes stored data collections such as libraries, file cabinets, and address books, when we talk about databases we almost invariably mean a collection of data that is stored on a computer. There are two basic categories of database. The most commonly encountered category is the transactional database, used to store dynamic data, such as inventory contents, which is subject to change on an ongoing basis. The other category is the analytical database, used to store static data, such as geographical or chemical test results, which is rarely altered. A brief history of the database: The first attempts at computer databases arose around the mid-twentieth century. Early versions were file-oriented. A database file became known as a table because its structure was the same as a paper-based data table. For the same reason, the columns within a table were called fields and the rows were called records. Computers were evolving during that same time period, and their potential for data storage and retrieval was becoming recognized. The earliest computer databases were based on a flat file model, in which records were stored in text format. In this model, no relationships are defined between records. Without defining such relationships, records can only be accessed sequentially. For example, if you wanted to find the record for the fiftieth customer, you would have to go through the first 49 customer records in sequence first. The flat file model works well for situations in which you want to process all the records, but not for situations in which you want to find specific records within the database. The hierarchical model, widely used in mainframe environments, was designed to allow structured relationships that would facilitate data retrieval. Within an inverted tree structure, relationships in the hierarchical model are parent-child and one-to-many. Each parent table may be related to multiple child tables, but each child table can only be related to a single parent table. Because table structures are permanently and explicitly linked in this model, data retrieval was fast. However, the model's rigid structure causes some problems. For example, you can't add a child table that is not linked to a parent table: if the parent table was "Doctors" and the child table was "Patients," you could not add a patient record independently. That would mean that if a new patient came into a community's health care system, under this system, their record could not be added until they had a doctor. The hierarchical structure also means that if a record is deleted in a parent table, all the records linked to it in child tables will be deleted as well. Also based on an inverted tree structure, the next approach to database design was the network model. The network model allowed more complex connections than the hierarchical model: several inverted trees might share branches, for example. The model connected tables in sets, in which a record in an owner table could link to multiple records in a member table. Like the hierarchical model, the network model enabled very fast data retrieval. However it also had a number of problems. For example, a user would need a clear understanding of the database structure to be able to get information from the data. Furthermore, if a set structure was changed, any reference to it from an external program would have to be changed as well. A database stores electronic data in an organized and accessible manner. The size and scope of databases can vary wildly, from a small database used by an individual to file phone numbers, to an extremely large enterprise database that stores several terabytes of information accessed by tens of thousands of individuals. A database's tables and rows hold data in much the same way as a file cabinet or an address book, but they allow users more flexibility in what kinds of searches they can perform on the data as well as how they want to view the data. [1]
What is a DBMS? A Database Management System (DBMS) is a software system that is used both to create databases and manage the information stored within them. The architecture of the DBMS will frequently determine or limit the possible uses of the databases it creates. Some DBMS's work best for creating single-user databases, while others can build databases that accommodate multiple users in larger corporate environments. [2]
What is a DBA? A Database Administrator (DBA) is crucial to any organization that has mission-critical information stored in its databases. DBAs are responsible for the design and administration of databases, and for ensuring that the highest level of data integrity is maintained. Database maintenance includes performance tuning, monitoring the logs for errors, performing backup and recovery procedures as well as tasks associated with the data stored in the database, which include data transfer, data replication and data cleansing. [3]
Database Architectures—RDBMS, OODBMS, and ORDBMS A database consists of one or more tables, each containing data stored as individual records. Different database architectures determine how the tables and records are organized or related to one another. The first database architectures - Hierarchical and Networked - have largely been superseded by the Relational, Object-Oriented and Object-Relational architectures.
The Relational Data Model, developed by Todd Codd in 1969, allows multiple tables to be related to one another within a database. [4] For example, one customer's information could be recorded in separate tables such as "Personal Information", "Marketing Efforts", and "Service Requests". The information stored in these tables will then relate back to the customer's main record. A relational database management system (RDBMS) also offers flexibility in terms of how the customer's data can be viewed. [5] To access the information stored in relational databases, users can either build queries using the Structured Query Language (SQL), or they can utilize a user interface that translates their requests into SQL and displays the results. While the American National Standards Institute (ANSI) approved an early version of SQL as a standard, many RDBMS's also use customized, proprietary forms of the language.
The Object-Oriented database model emerged in the mid-1980s due to the dissatisfaction of some database users with the structural limitations of RDBMS's. The Object-Oriented model defines each piece of data and its associated processes as an individual object. According to the basic tenets of this model, all information about an object is stored in one place instead of being stored across multiple tables, as is done in the relational model. [6] An Object-Oriented Database Management System (OODBMS) also integrates more easily with applications that have been written with an Object-Oriented programming language such as C++ or Java. Despite the advantages of the Object-Oriented approach, no standard model for the construction of an OODBMS yet exists. For this reason, at least in part, RDBMS's still dominate the database market.
One effort to combine the best parts of the RDBMS and OODBMS is the Object-Relational Database Management System (ORDBMS). This model allows developers to incorporate the best parts of an RDBMS and an ODBMS. An ORDBMS works with objects like an ODBMS, but also allows SQL-based querying like an RDBMS.
Market Leaders
The Future of Databases
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Copyright © 2003 Tony Hogan |
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