Heuristic optimization often includes making transformations to the query tree by moving operators up and down the tree so that the transformed tree is equivalent to the tree before the transformations. Before we discuss these heuristics, it is necessary to discuss the following rules governing the manipulation of relational algebraic expressions: 1. Joins and Products … Read more
Before query optimization is carried out, one would of course need to decide what needs to be optimized. The goal of achieving efficiency itself may be different in different situations. For example, one may wish to minimize the processing time but in many situations one would wish to minimize the response time. In other situations, … Read more
In most database systems, queries are posed in a non-procedural language like SQL and as we have noted earlier such queries do not involve any reference to access paths or the order of evaluation of operations. The query processing of such queries by a DBMS usually involves the following four phases: 1. Parsing 2. Optimization … Read more
SQL language also includes syntax to update, insert, and delete records. These query and update commands together form the Data Manipulation Language (DML) part of SQL: • INSERT INTO – inserts new data into a database table • UPDATE – updates data in a database table • DELETE – deletes data from a database table … Read more
Once entities and relationships have been identified and defined, the first draft of the entity relationship diagram can be created. This post introduces the ER diagram by demonstrating how to diagram binary relationships. Recursive relationships are also shown. Binary Relationships Figure 1 shows examples of how to diagram one-to-one, one-to-many, and many-to- many relationships. Figure … Read more
The data model is one part of the conceptual design process. The other is the function model. The data model focuses on what data should be stored in the database while the function model deals with how the data is processed. To put this in the context of the relational database, the data model is … Read more
The Entity-Relationship (ER) model was originally proposed by Peter in 1976 as a way to unify the network and relational database views. Simply stated the ER model is a conceptual data model that views the real world as entities and relationships. A basic component of the model is the Entity-Relationship diagram which is used to … Read more
Database design is defined as: “design the logical and physical structure of one or more databases to accommodate the information needs of the users in an organization for a defined set of applications”. The design process roughly follows five steps: 1. Planning and analysis 2. Conceptual design 3. Logical design 4. Physical design 5. Implementation … Read more
A primary goal of a database system is to retrieve information from and store new information in the database. People who work with a database can be categorized as database users or database administrators. Database Users and User Interfaces There are four different types of database-system users, differentiated by the way they expect to interact … Read more
We can define a data dictionary as a DBMS component that stores the definition of data characteristics and relationships. You may recall that such “data about data” were labeled metadata. The DBMS data dictionary provides the DBMS with its self describing characteristic. In effect, the data dictionary resembles and X-ray of the company’s entire data … Read more