A relational database is a type of database that stores and provides access to data points that are related to one another. Relational databases are based on the relational model, an intuitive, straightforward way of representing data in tables. In a relational database, each row in the table is a record with a unique ID called the key. A relational database definition (database schema, sometimes referred to as a relational schema) can thus be thought of as a collection of named relation schemas. 7 8 In implementations, the domain of each attribute is effectively a data type 9 and a named relation schema is effectively a relation variable ( relvar for short).
- Relational Vs Non Relational Database
- Relational Database Management System Example
- Relational Databases 101
Building a system in Oracle or some other relational database product does not automatically make it a relational database. Similarly, you can design a perfectly good relational database and implement it in something other than a relational database product. We discuss two important areas:
A relational database is a collection of data items with pre-defined relationships between them. These items are organized as a set of tables with columns and rows. Tables are used to hold information about the objects to be represented in the database. Relational database design: relationships explained. Getting to know what is a relational database, you will notice the term itself is very revealing: a relational database is one that allows database relationships. It’s rather common for a database of this type to have up to thousands of tables.
- What do people mean by relational database?
- What is the Oracle relational database product?
What makes a database “relational”?
When a database is described as relational, it has been designed to conform (at least mostly) to a set of practices called the rules of normalization. A normalized database is one that follows the rules of normalization.
For example, in an organization, you have employees who work in specific departments. Each employee and department has a number and a name. You could organize this information as shown in Table 1.
Table 1: Sample Employee Information
EmpNo | Ename | DeptNo | DeptName |
101 | Abigail | 10 | Marketing |
102 | Bob | 20 | Purchasing |
103 | Carolyn | 10 | Marketing |
104 | Doug | 20 | Purchasing |
105 | Evelyn | 10 | Marketing |
If you structure your data this way and make certain changes to it, you’ll have problems. For example, deleting all the employees in the Purchasing department will eliminate the department itself. If you change the name of the Marketing department to “Advertising,” you would need to change the record of each employee in that department.
Using the principles of relational databases, the Employee and Department data can be restructured into two separate tables (DEPT and EMP), as shown in Tables 2 and 3.
Table 2: A Sample Relational DEPT Table
DeptNo | DeptName |
10 | Marketing |
20 | Purchasing |
Table 3: A Sample Relational EMP Table
EmpNo | EName | DeptNo |
101 | Abigail | 10 |
102 | Bob | 20 |
103 | Carolyn | 10 |
104 | Doug | 20 |
105 | Evelyn | 10 |
By using this structure, you can examine the EMP table to find out that Doug works in department 20. Then you can check the DEPT table to find out that department 20 is Purchasing. You might think that Table 1 looks more efficient. However, retrieving the information you need in a number of different ways is much easier with the two-table structure. Joining the information in the two tables for more efficient retrieval is exactly the problem that relational databases were designed to solve.
When the tables are implemented in the database, the information in the two tables is linked by using special columns called foreign keys. In the example, the DeptNo column is the foreign key linking the Department and Employee tables.
Tables 4 and 5 show another common database structure, namely a purchase order (PURCH_ORDER table) for an item and the information details associated with the purchase order (PURCH_ORDER_DTL table).
Table 4: A Sample Relational PURCH_ORDER Table
PO_Nbr | Date |
450 | 12/10/2006 |
451 | 2/26/2006 |
452 | 3/17/2006 |
453 | 6/5/2006 |
Table 5: A Sample Relational PURCH_ORDER_DTL Table
PO_Nbr | Line_Nbr | Item | Qty | Price |
450 | 1 | Hammer | 1 | $10.00 |
451 | 1 | Screwdriver | 1 | $8.00 |
451 | 2 | Pliers | 2 | $6.50 |
451 | 3 | Wrench | 1 | $7.00 |
452 | 1 | Wrench | 3 | $7.00 |
452 | 2 | Hammer | 1 | $10.00 |
453 | 1 | Pliers | 1 | $6.50 |
A purchase order can include many items. Table 5 shows that Purchase Order 451 includes three separate items. The link (foreign key) between the tables is the Purchase Order Number.
Understanding basic database terminology
Relational Vs Non Relational Database
A database consists of tables and columns, as described in the preceding section. There are some other terms you need to know in order to understand how databases work. A database is built in two stages. First you create a logical data model to lay out the design of the database and how the data will be organized. Then you implement the database according to the physical data model, which sets up the actual tables and columns. Different terminology applies to the elements of the logical and physical designs. In addition, relational database designers use different words from object-oriented (OO) database designers to describe the database elements. Table 6 shows the words used in each of these cases.
Table 6: Database Design Terminology
Logical/Relational | Logical/Object-Oriented | Physical Implementation |
Entity | Class | Table |
Attribute | Attribute | Column |
Instance | Object | Row |
Relational Database Management System Example
The definitions of the words in Table 6 are as follows:
- Entity: An entity corresponds to something in the real world that is of interest and that you want to store information about. Examples of entities include things such as departments within an organization, employees, or sales. Each specific department or employee is considered an instance of that entity. For example, in Table 3, Doug is an instance of the entity Employee. (In the OO world, Doug would be an object in the Employee class.)
- Attribute: This word is used in both relational and OO databases to represent information about an entity instance or an object that will be tracked. An example of an attribute might be the birth date or Social Security number of an employee.
- Entities (classes), their attributes, and instances (objects): These are implemented in the database as tables, columns, and rows respectively.
One additional important concept to understand when dealing with relational databases is the primary key. A primary key uniquely identifies a specific instance of an entity. No two instances of an entity can have the same primary key. The values of all parts of the primary key must never be null. The most common types of primary keys in relational databases are ID numbers. For example, in Table 3, the EmpID can be the primary key. Sometimes more than one attribute (or sets of attributes) can be used as a primary key. These attributes are called candidate keys, one set of which must be designated as the primary key.
Databases have been a staple of business computing from the very beginning of the digital era. In fact, the relational database was born in 1970 when E.F. Codd, a researcher at IBM, wrote a paper outlining the process. Since then, relational databases have grown in popularity to become the standard.
Originally, databases were flat. This means that the information was stored in one long text file, called a tab delimited file. Each entry in the tab delimited file is separated by a special character, such as a vertical bar (|). Each entry contains multiple pieces of information (fields) about a particular object or person grouped together as a record. Quickpick 2 1 2 – seamless document launcher. The text file makes it difficult to search for specific information or to create reports that include only certain fields from each record. Here's an example of the file created by a flat database:
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Lname, FName, Age, Salary|Smith, John, 35, $280|Doe, Jane, 28, $325|Brown, Scott, 41, $265|Howard, Shemp, 48, $359|Taylor, Tom, 22, $250
You can see that you have to search sequentially through the entire file to gather related information, such as age or salary. A relational database allows you to easily find specific information. It also allows you to sort based on any field and generate reports that contain only certain fields from each record. Relational databases use tables to store information. The standard fields and records are represented as columns (fields) and rows (records) in a table.
With a relational database, you can quickly compare information because of the arrangement of data in columns. The relational database model takes advantage of this uniformity to build completely new tables out of required information from existing tables. In other words, it uses the relationship of similar data to increase the speed and versatility of the database.
The 'relational' part of the name comes into play because of mathmatical relations. A typical relational database has anywhere from 10 to more than 1,000 tables. Each table contains a column or columns that other tables can key on to gather information from that table.
Relational Databases 101
By storing this information in another table, the database can create a single small table with the locations that can then be used for a variety of purposes by other tables in the database. A typical large database, like the one a big Web site, such as Amazon would have, will contain hundreds or thousands of tables like this all used together to quickly find the exact information needed at any given time.
Home design 3d 4 0 5. Relational databases are created using a special computer language, structured query language (SQL), that is the standard for database interoperability. SQL is the foundation for all of the popular database applications available today, from Access to Oracle.
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