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A Database is a collection of logically related data designed to meet the information needs of one or more users. The term originated within the computer industry, but its meaning has been broadened by popular use, to the extent that the European Database Directive (which creates intellectual property rights for databases) includes non-electronic databases within its definition. This article is confined to a more technical use of the term; though even amongst computing professionals, some attach a much wider meaning to the word than others.
A possible definition is that a database is a collection of records stored in a computer in a systematic way, so that a computer program can consult it to answer questions. For better retrieval and sorting, each record is usually organized as a set of data elements (facts). The items retrieved in answer to queries become information that can be used to make decisions. The computer program used to manage and query a database is known as a database management system (DBMS). The properties and design of database systems are included in the study of information science.
The central concept of a database is that of a collection of records, or pieces of knowledge. Typically, for a given database, there is a structural description of the type of facts held in that database: this description is known as a schema. The schema describes the objects that are represented in the database, and the relationships among them. There are a number of different ways of organizing a schema, that is, of modeling the database structure: these are known as database models (or data models). The model in most common use today is the relational model, which in layman's terms represents all information in the form of multiple related tables each consisting of rows and columns (the true definition uses mathematical terminology). This model represents relationships by the use of values common to more than one table. Other models such as the hierarchical model and the network model use a more explicit representation of relationships.
Strictly speaking, the term database refers to the collection of related records, and the software should be referred to as the database management system or DBMS. When the context is unambiguous, however, many database administrators and programmers use the term database to cover both meanings.
Many professionals would consider a collection of data to constitute a database only if it has certain properties: for example, if the data is managed to ensure its integrity and quality, if it allows shared access by a community of users, if it has a schema, or if it supports a query language. However, there is no agreed definition of these properties.
Database management systems are usually categorized according to the data model that they support: relational, object-relational, network, and so on. The data model will tend to determine the query languages that are available to access the database. A great deal of the internal engineering of a DBMS, however, is independent of the data model, and is concerned with managing factors such as performance, concurrency, integrity, and recovery from hardware failures. In these areas there are large differences between products.
In computer science, data modeling is the process of structuring and organizing data. These data structures are then typically implemented in a database management system. In addition to defining and organizing the data, data modeling may also impose constraints or limitations on the data placed within the structure.
Managing large quantities of structured and unstructured data is a primary function of information systems. Data models describe structured data for storage in data management systems such as relational databases. They typically do not describe unstructured data, such as word processing documents, email messages, pictures, digital audio, and video. Early phases of many software development projects emphasize the design of a conceptual data model. Such a design can be detailed into a logical data model. In later stages, this model may be translated into physical data model.
Database design is the process of producing a detailed data model of a database. This logical data model contains all the needed logical and physical design choices and physical storage parameters needed to generate a design in a Data Definition Language, which can then be used to create a database. A fully attributed data model contains detailed attributes for each entity.
The term database design can be used to describe many different parts of the design of an overall database system. Principally, and most correctly, it can be thought of as the logical design of the base data structures used to store the data. In the relational model these are the tables and views. In an object database the entities and relationships map directly to object classes and named relationships. However, the term database design could also be used to apply to the overall process of designing, not just the base data structures, but also the forms and queries used as part of the overall database application within the database management system (DBMS).[1]
The process of doing database design generally consists of a number of steps which will be carried out by the database designer. Usually, the designer must:
Determine the relationships between the different data elements.
Superimpose a logical structure upon the data on the basis of these relationships.[2]
In computer science, an entity-relationship model (ERM) is a model providing a high-level description of a conceptual data model. Data modeling provides a graphical notation for representing such data models in the form of entity-relationship diagrams (ERD). The first stage of information system design uses these models to describe information needs or the type of information that is to be stored in a database during the requirements analysis. The data modeling technique can be used to describe any ontology (i.e. an overview and classifications of used terms and their relationships) for a certain universe of discourse (i.e. area of interest). In the case of the design of an information system that is based on a database, the conceptual data model is, at a later stage (usually called logical design), mapped to a logical data model, such as the relational model; this in turn is mapped to a physical model during physical design. Note that sometimes, both of these phases are referred to as "physical design".
There are a number of conventions for entity-relationship diagrams (ERDs). The classical notation is described in the remainder of this article, and mainly relates to conceptual modelling. There are a range of notations more typically employed in logical and physical database design, including information engineering, IDEF1x (ICAM DEFinition Language) and dimensional modelling.
A logical data model typically includes all the entities and their attributes that correspond to a set of specified information requirements, which includes the definition of logical constraints on these attributes: primary, alternate key, foreign key, subtyping, data types, and domain of valid values.
The purpose of a logical data model is: a) to give a normalized and graphical representation of the scoped business data requirements and related data business rules to the stakeholders; b) promote understanding and communication between stakeholders and the modeler; c) correct and validate the assumptions about the scope specifications of the data related requirements and business rules.
It is not intended to be a representation of a physical database. It is typically produced early in system design, it the successor to a conceptual data model, and it is frequently a precursor to the physical data model that documents the DBMS-dependent design of a database, schema, or portion thereof, and its actual implementation.
SQL is commonly spoken in initialism-style ess-cue-el (see English alphabet) — regarded as more formal — or in a phonetically-amalgamated form that mirrors the English word sequel. Concerning the names of major database products (or projects) containing the letters SQL, each has its own convention: MySQL is officially and commonly pronounced "My Ess Cue El"; PostgreSQL is expediently pronounced postgres; and Microsoft SQL Server is commonly spoken as Microsoft-sequel-server.
This unique SQL Tutorial is the "sequel" to the highly successful SQLCourse.com site and will provide you with more advanced easy-to-follow SQL Instruction and the ability to practice what you learn on-line with immediate feedback! You will receive immediate results on a web page after submitting your SQL Commands.
This continuation course will provide you with critical need-to-know advanced features and clauses of the SELECT statement that weren't supported in the previous SQLCourse.com site. Everything you learn here will be ANSI SQL compliant and should work with most SQL databases such as Oracle, SQL Server, mySQL, MS Access, Informix, Sybase, or any other ANSI SQL compliant database.
If you're already familar with the basics of SQL, you can still use this as a refresher, and practice some SQL statements.
The client–server model of computing is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients.[1] Often clients and servers communicate over a computer network on separate hardware, but both client and server may reside in the same system. A server machine is a host that is running one or more server programs which share their resources with clients. A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await incoming requests.
Exam
70-229, Second Edition
Author Microsoft Corporation
Pages 880
Disk 1 Companion CD(s); 1 Evaluation CD(s)
Level Int/Adv
Published 05/07/2003
ISBN 0-7356-1960-3
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A Data Warehouse is a computerdatabase that collects, integrates and stores an organization's data with the aim of producing accurate and timely management information and supporting data analysis.
Performance - Ensuring maximum performance given budgetary constraints
Development and testing support - Helping programmers and engineers to efficiently utilize the database.
The role of a database administrator has changed according to the technology of database management systems (DBMSs) as well as the needs of the owners of the databases. For example, although logical and physical database design are traditionally the duties of a database analyst or database designer, a DBA may be tasked to perform those duties.
Collections of data (eg. in a database) can be distributed across multiple physical locations. A distributed database is distributed into separate partitions/fragments. Each partition/fragment of a distributed database may be replicated (ie. redundant fail-overs, RAID like).
Besides distributed database replication and fragmentation, there are many other distributed database design technologies. For example, local autonomy, synchronous and asynchronous distributed database technologies. These technologies' implementation can and does definitely depend on the needs of the business and the sensitivity/confidentiality of the data to be stored in the database. And hence the price the business is willing to spend on ensuring data security, consistency and integrity.
An Object Database is a database in which information is represented in the form of objects. The database management system for an object database is referred to variously as a ODBMS or OODBMS (object-oriented database management system).
There are two main factors that lead users to adopt object database technology. Firstly, a relational database becomes cumbersome to use with complex data. Secondly, data is generally manipulated by application software written using object-oriented programming languages and tools such as C++, Java, Borland Delphi and C#, and the code needed to translate between this representation of the data and the tuples of a relational database can be tedious to write, and time-consuming to execute. This mismatch between the models used to represent information in the application programs and the database is sometimes referred to as an impedance mismatch.
One can refer to the Oracle database management system unambiguously as Oracle DBMS or (since it manages databases which have relational characteristics) as Oracle RDBMS.
when it refers nowadays to the Oracle RDBMS (the software it sells for the purpose of managing databases) as the Oracle Database. The distinction between the managed data (the database) and the software which manages the data (the DBMS / RDBMS) relies, in Oracle's marketing literature, on the capitalisation of the word database.
Oracle Corporation produces and markets the Oracle DBMS, which many database applications use extensively on many popular computing platforms.
Larry Ellison and his friends and former co-workers Bob Miner and Ed Oates - who had started a consultancy called Software Development Laboratories (SDL) - developed the original Oracle DBMS software. They called their finished product Oracle after the code name of a CIA-funded project they had worked on while previously employed by Ampex.
