Shree Secondary School

Relational algebra: Relational Algebra is a procedural language that is performed on one or more existing relation to derive result relations without changing the original relation and can be used to tell the   DBMS   how to build a new relation from one or more relations in the database. So, it defines a complete scheme for each of  the result relations. While using the relational algebra, user has to specify what is required and what are the procedures or steps to obtain the required output The relational algebra is a theoretical language with operations that work on one or more relations to define another relation without changing the original relation(s). Thus, both the operands and the results are relations, and so the output from one operation can become the input to another operation. This allows expressions to be nested in the relational algebra, just as we can nest arithmetic operations. This property is called closure: relations are closed under the alg...

Unit 1:           Introduction to Database System Architecture   What is Data? Data is a singular form of "Datum" is a collection of facts and figure, such as numbers, words, measurements, observations or even just descriptions of things. Data can be collected in many ways. The simplest way is direct observation. Example: you want to find how many cars pass by a certain point on a road in a 10-minute interval. So: stand at that point on the road, and count the cars that pass by in that interval.  We collect data by doing a Survey. There are two types of Data Qualitative: Qualitative data is descriptive information (it describes something) Quantitative: Quantitative data, is numerical information (numbers). Quantitative data can also be Discrete or Continuous: Discrete data can only take certain values (like whole numbers) Continuous data...