The relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by Edgar F. Codd. In the relational model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is a relational database.
The purpose of the relational model is to provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries.
Most relational databases use the SQL data definition and query language; these systems implement what can be regarded as an engineering approximation to the relational model. A table in an SQL database schema corresponds to a predicate variable; the contents of a table to a relation; key constraints, other constraints, and SQL queries correspond to predicates. However, SQL databases, including DB2, deviate from the relational model in many details, and Codd fiercely argued against deviations that compromise the original principles.
The Internet is a global system of interconnected computer networks that use the standard
Internet protocol suite (often called TCP/IP, although not all applications use TCP) to
serve billions of users worldwide. It is a network of networks that consists of millions of
private, public, academic, business, and government networks, of local to global scope,
that are linked by a broad array of electronic, wireless and optical networking technologies.
The Internet carries an extensive range of information resources and services, such as the
inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure
to support email.
Internet is a short form of the technical term internet work, the result of interconnecting
computer networks with special gateways or routers. The Internet is also often referred to
as the Net.
The terms Internet and World Wide Web are often used in everyday speech without much
distinction. However, the Internet and the World Wide Web are not one and the same. The
Internet establishes a global data communications system between computers. In contrast,
the Web is one of the services communicated via the Internet. It is a collection of
interconnected documents and other resources, linked by hyperlinks and URLs
The class is at the core of Java. It is the logical construct upon which the entire Java language is built because it defines the shape and nature of an object. As such,the class forms the basis for object-oriented programming in Java. Any concept you wish to implement in a Java program must be encapsulated within a class. Perhaps the most important thing to understand about a class is that it defines a new data type. Once defined, this new type can be used to create objects of that type. Thus, a class is a template for an object, and an object is an instance of a class. Because an object is an instance of a class, you will often see the two words object and instance used interchangeably.
A network consists of two or more computers that are linked in order to share resources
(such as printers and CDs), exchange files, or allow electronic communications. The
computers on a network may be linked through cables, telephone lines, radio waves,
satellites, or infrared light beams.
Two very common types of networks include:
Local Area Network (LAN)
Wide Area Network (WAN)
You may also see references to a Metropolitan Area Networks (MAN), a Wireless LAN
(WLAN), or a Wireless WAN (WWAN).
Networking is just what it says; setting up a network where you can meet people working in your field of interest. If you ask people around you if they know someone in the field you are interested in, you will be surprised by the number of referrals you can get. Calling someone at a company that you have a connection with through a friend makes it easier to get your foot in the door of that company.
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