In order to convert a table to BCNF, we must : Find and remove the overlapping candidate keys. Place the part of the candidate key and the attribute it is functionally dependent on, in a different table. Group the remaining items into a table. Hence,from the PROJECT table( refer to the Boycee-Codd Normal Form [...]
Continue reading → The original definition of 1NF was inadequate in some situations. It was not satisfactory for the tables: That had multiple candidate keys. Where the multiple candidate keys were composite Where the multiple candidate keys overlapped (had atleast one attribute to common) Therefore, a new normal form, the BCNF was introduced. You must understand that [...]
Continue reading → Inorder to convert a table into 3NF we must : Find and remove non-key attributes that are functionally dependent on attributes that are not the primary key. Place them in a different table. Group the remaining attributes. As for example, to convert the table Employee ( refer to the Third Normal Form (3NF) link : http://churmura.com/third-normal-form-3nf/) into [...]
Continue reading → A table is said to be in 3NF when it is in 2NF and every non-key attributes is functionally dependent only on the primary key. Consider the table EMPLOYEE The problems with dependencies of this kind are: Insertion : The department head of a new department that does not have any employees at present cannot [...]
Continue reading → Inorder to convert a table into 2NF, we must : Find and remove attributes that are functionally dependent on only a part of the key and not on the whole key. Place them in a different table. Group the remaining attributes. To convert the table PROJECT( refer the Second Normal form (2NF) Link : http://churmura.com/second-normal-form-2nf/) into [...]
Continue reading → A table is said to be in 2NF when it is in 1NF and every attribute in the row is functionally dependent upon the whole key, and not just part of the key. Consider the PROJECT table . The table has the following rows : This situation could lead to the following problems : Insertion [...]
Continue reading → The normalization theory is based on the fundamental notion of fundamental dependency. First, let’s examine the concept of functional dependency. Given a relation R, attribute A is functionally dependent on attribute B if each value of A in R is associated with precisely one value of B. In other words, attribute A is functionally dependent [...]
Continue reading → A table is said to be in the 1 NF when each cell of the table contains precisely one valid. Consider the following table PROJECT. PROJECT The data in the table is not normalized because the cells in PRJCODE and HOURS have more than one value. By applying the 1NF definition to the PROJECT table, [...]
Continue reading → Normalization is scientific method of breaking down complex table structures into simple table structures by using certain rules. Using this method, you can, reduce redundancy in a table and eliminate the problems of inconsistency and disk space usage. You can also ensure that there is no lose of information. Normalization has several benefits. It enables [...]
Continue reading → An RDBMS uses associative addressing; that is, it identifies and locates rows by value. The physical address is transparent to the user. Therefore, relational systems require keys that can uniquely identify the rows of a table. There are various types of keys, some of which we are already familiar with. These are Primary Foreign Candidate [...]
Continue reading → The conceptual model reflects entities and their relationships based on the data processing needs of an organization. To develop a database that satisfies the information needs of the present as well as the future, you must design a conceptual model of the database first. The conceptual model design is not concerned with the implementation and operation [...]
Continue reading → A storage manager is a program module that provides the interface between the lowlevel data stored in the database and the application programs and queries submitted to the system. The storage manager is responsible for the interaction with the file manager. The raw data are stored on the disk using the file system, which is [...]
Continue reading → INTERSECT: The Intersect operator builds a relation consisting of tuples that appear in both relations. Consider tables A and B. Nancy is doing a double major; therefore, her name appears in both tables. An intersect operation on tables A and B extracts the row common to both relations. The INTERSECT operations works on union compatible [...]
Continue reading → The relational model is based on the principle of relational algebra. Relational algebra is a collection of operators that operate on relations. Each operator takes one or two relations as its input and produces a new relation as its output. RESTRICT: The Restrict operator extracts specified tuples or rows from a given relation, based on [...]
Continue reading → One major difference between the relational model and earlier data models is that explicit pointers such as parent -child relationships of the hierarchical model are banned from the relational model. Yet , relationships do exist in the relational model. However, these relationships are represented by common data values stored in two or more tables. All [...]
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