Reviewing basic concepts of relational database
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The document discusses the basics of relational databases. It defines what a database is, the advantages it provides over file-based data storage, and some disadvantages. It also covers relational database concepts like tables, records, fields, keys, and normalization. The document explains how to design a relational database by determining the purpose and entities, modeling relationships with E-R diagrams, and following steps to normalize the data.
Reviewing basic concepts of relational database
- 1. Reviewing Basic Concepts of Relational Database Prof. Hitesh Mohapatra
- 2. Why there is need of database? • Multiple file with the same content. • Multiple file with different content but with same name. • Updation of information into multiple files. • Data are stored at multiple locations.
- 3. What is database? • A Database is a system that allows everyone to share, manage and use data. • Reduces data redundancy • Reduces updating errors and increased consistency • Greater data integrity and independence from applications programs • Improvises data access to users through use of host and query languages • Improves data security • Reduces data entry, storage, and retrieval costs • Facilitated development of new applications program Database
- 4. What are the disadvantages of database? • Database systems are complex, difficult, and time-consuming to design • Substantial hardware and software start-up costs • Damage to database affects virtually all applications programs • Extensive conversion costs in moving form a file- based system to a database system • Initial training required for all programmers and users
- 5. What are the types of databases available? • Hierarchical Data Model, in which there is a tree-like relationship between data. • Network Data Model, in which pieces of data have overlapping relationships with each other. • Relational Data Model, process data using the easy- to-understand concept of table.
- 6. What is a Relational Database? • A relational database is a type of database. • It uses a structure that allows us to identify and access data in relation to another piece of data in the database. • Data in a relational database is organized into tables.
- 7. Table, Record, Field, Row & Column • A table is a set of data elements (values). • A piece of data in a file is called a record. • Each item in a record is called a field. • One piece of data or record is called a row. • Each item or field is called a column.
- 8. Types of keys • Key: One or more columns in a database table that is used to sort and/or identify rows in a table. e.g. if you were sorting people by the field salary then the salary field is the key. • Primary key: A primary key is a one or more fields that uniquely identifies a row in a table. The primary key cannot be null (blank). The primary key is indexed (more on index later). • Foreign key: A foreign key is a relationship between columns in two database tables (one of which is indexed) designed to insure consistency of data. • Composite key: A primary key composed of one or more columns. The primary key can be formed using the fields (though not very advisable). • Natural key: A composite primary key which is composed of attributes (fields) which already exist in the real world (for example First Name, Last Name, Social Security Number). • Surrogate key: A primary key which is internally generated (typically auto-incremental integer value) that does not exist in the real world (for example, ID which serves to identify the record but nothing else). • Candidate key: A column, or set of columns, in a table that can uniquely identify any database record without referring to any other data. Each table may have one or more candidate keys, but one candidate key is unique (the primary key). • Compound key: A composite key consisting of two or more fields that uniquely describe a row in a table. The difference between compound and candidate is that all of the fields in the compound key are foreign keys; in the candidate key one or more of the fields may be foreign keys (but it is not mandatory).
- 9. How to design a database? When you try to create a database yourself, the first step is to determine the conditions of the data you are trying to model.
- 10. The E-R model E refers Entity. A recognizable object in the real world. For example, when exporting fruits to other countries, fruit and export destination can be considered entities. Represented with a rectangle. • Each entity has attributes, particular properties that describe the entity (Product Name in Fruit, for example). Represented with an ovallus.
- 11. • R refers relationship. How entities relate with each other. For example, fruits and export destination are associated with each other because you sell fruits to export destinations. Represented with a diamond. Fruit is exported to many Export destinations and Export destination purchases many kinds of fruit. We call this a many-to-many relationship. In the E-R model the number of associations between entities is considered, this is called cardinality.
- 12. • Cardinality: Number of associations between entities. • One-to-one relationship (1-1): I only sell fruits to you and you only buy fruits from me. • One-to-many (or many-to-one) relationship (n-1 or 1-n): I sell fruits to other families and those families buy fruits only from me. • Many-to-many relationship (n-n): You have an example above.
- 13. Normalization Process of tabulating data from the real world for a relational database, following a series of steps. It is necessary to Normalize data in order to properly manage a relational database. Normalization is used for mainly two purposes: • Eliminating redundant(useless) data. • Ensuring data dependencies make sense i.e. data is logically stored.
- 14. Steps for designing a database • Determine the purpose of the database. • Determine the tables needed. • Identify needed fields. • Identify exclusive fields. • Determine relations between tables. • Define constraints to preserve data integrity (don't forget normalization).