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Rdbms stands for Relational database management system.It uses tables(relations) for storing the data.In mathematical terms these tables are called relations.
Matteo Kunze
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What is the major advantage of using a Database for storing and managing data?
Computers store and process data of three basics types :numbers or word and symbols(audio and pictures and videos are stored but are not basic) Programs like Word and Excel specialized in building documents which can be quite large) and can handle the requirements of many small businesses. But when you are a large business or government entity with thousands or millions of customers you also need a means for sorting client data after it is entered. That type of sorting starts with a "query" which is set of command to define the sort process. The programs that do this are call RDBM"S; relational data base managers.
If a table has foreign keys which normal form is it in?
A foreign key is determined by the underlying database model. Usually, a foreign key points to the "primary key" of the table that it references. In Access, for example, a lookup field holds the ID of the record you are referencing, while displaying whichever field you specify from the referenced table. In MySQL and most other RDBM systems, you can query the data using a LEFT JOIN or RIGHT JOIN based using the form "a.relatedid = b.id", where "a" is an alias to the child record (the one with the lookup field), and "b" is the primary key on the parent record.A query on a foreign key might look like this: "select * from `orders` a left join `customers` b on a.`customerid` = b.`id`". In this query, you would see the order plus the customer that placed the order, each order on it's own line. Customers may be duplicated, since they might have multiple orders in the database. Of course, this assumes that "customerid" is the field on the "orders" table that contains the foreign key relationship, and "id" is a primary key on the "customers" table.The primary key must be unique to be useful. This is usually defined as an AUTO_INCREMENT field, but it may also be some other value guaranteed to be unique, such as a randomly assigned UUID or customer number.
What are the main characteristics of a relational model?
The main characteristics of this "databases" is that the belief that what is mathematically elegant, is also the simplest and best. So the relational model is based on relational calculus, where you see the database as "relations" of tuples, where each tuple represent elements of data. You then go on and describe addition, subtraction (insert, delete), multiplication (join) and division (inner join) as operators on tuples, and projection as operators on elements. <p> This works fine, and a RDBM has to support integrity constraints that ensures that the mathematical properties are retained. If you do not like calculus, you can also describe the RDBMS with "relational algebra". A more pragmatic way of structuring data, that was intended to reflect the use of data can be found in the CODASYL DBTG proposal. Such databases will be vastly more efficient, there will be things you cannot do, whereas all can be done with a relational database - somehow.Note that a database as such is based on assumptions of support to retain consistency, data is supposed to never be lost, and when you make changes, you are able to "commit" them all because they are in the application logic defined so that it is not one, but all changes or none. If you do not manage to complete the application logic, every single trace of the changes is to be removed - "undone". A database shall also support multiple users at once, and see to that your changes are protected from others messing around with the data that you work on. This separate the various databases from using the plain file system. If you just make an application, the CODASYL database model will be much easier to work with, but when you later want to expand and add to the application, you will prefer to use the more general relational model, since this does not constrain you in any way.
