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Sunday 4 March 2012

SQL Commands:


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SQL commands are instructions used to communicate with the database to perform specific task that work with data. SQL commands can be used not only for searching the database but also to perform various other functions like, for example, you can create tables, add data to tables, or modify data, drop the table, set permissions for users. SQL commands are grouped into four major categories depending on their functionality:



Data Definition Language (DDL) - These SQL commands are used for creating, modifying, and dropping the structure of database objects. The commands are CREATE, ALTER, DROP, RENAME, and TRUNCATE.
Data Manipulation Language (DML) - These SQL commands are used for storing, retrieving, modifying, and deleting data. These commands are SELECT, INSERT, UPDATE, and DELETE.



Transaction Control Language (TCL) - These SQL commands are used for managing changes affecting the data. These commands are COMMIT, ROLLBACK, and SAVEPOINT.
Data Control Language (DCL) - These SQL commands are used for providing security to database objects. These commands are GRANT and REVOKE.



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Friday 2 March 2012

Introduction to the Oracle Database


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Oracle Database Architecture


An Oracle database is a collection of data treated as a unit. The purpose of a database is to store and retrieve related information. A database server is the key to solving the problems of information management. In general, a server reliably manages a large amount of data in a multiuser environment so that many users can concurrently access the same data. All this is accomplished while delivering high performance. A database server also prevents unauthorized access and provides efficient solutions for failure recovery.

Oracle Database is the first database designed for enterprise grid computing, the most flexible and cost effective way to manage information and applications. Enterprise grid computing creates large pools of industry-standard, modular storage and servers. With this architecture, each new system can be rapidly provisioned from the pool of components. There is no need for peak workloads, because capacity can be easily added or reallocated from the resource pools as needed.

The database has logical structures and physical structures. Because the physical and logical structures are separate, the physical storage of data can be managed without affecting the access to logical storage structures.





Overview of Oracle Grid Architecture


Grid computing is a new IT architecture that produces more resilient and lower cost enterprise information systems. With grid computing, groups of independent, modular hardware and software components can be connected and rejoined on demand to meet the changing needs of businesses.

The grid style of computing aims to solve some common problems with enterprise IT: the problem of application silos that lead to under utilized, dedicated hardware resources, the problem of monolithic, unwieldy systems that are expensive to maintain and difficult to change, and the problem of fragmented and disintegrated information that cannot be fully exploited by the enterprise as a whole.

Benefits of Grid Computing Compared to other models of computing, IT systems designed and implemented in the grid style deliver higher quality of service, lower cost, and greater flexibility. Higher quality of service results from having no single point of failure, a robust security infrastructure, and centralized, policy-driven management. Lower costs derive from increasing the utilization of resources and dramatically reducing management and maintenance costs. Rather than dedicating a stack of software and hardware to a specific task, all resources are pooled and allocated on demand, thus eliminating under utilized capacity and redundant capabilities. Grid computing also enables the use of smaller individual hardware components, thus reducing the cost of each individual component and providing more flexibility to devote resources in accordance with changing needs.




Oracle Database Application Development


SQL and PL/SQL form the core of Oracle's application development stack. Not only do most enterprise back-ends run SQL, but Web applications accessing databases do so using SQL (wrappered by Java classes as JDBC), Enterprise Application Integration applications generate XML from SQL queries, and content-repositories are built on top of SQL tables. It is a simple, widely understood, unified data model. It is used standalone in many applications, but it is also invoked directly from Java (JDBC), Oracle Call Interface (OCI), Oracle C++ Call Interface (OCCI), or XSU (XML SQL Utility). Stored packages, procedures, and triggers can all be written in PL/SQL or in Java.



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Ruchika Mandore  [ MCA ] 
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Thursday 1 March 2012

What is Cardinality


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Cardinality is the term used in database relations to denote the occurrences of data on either side of the relation. In the common data architecture, cardinality is documented with data integrity but not with data structure.

There are several types of cardinality defining relationships between occurrences of entities on two sides of the line of relationships.

The Link Cardinality is a 0:0 relationship and defined as one side does not need the other to exists. For example, in a person and parking space relationship, it denotes that I do not need to have a person to have a parking space and I don’t need a parking space to have a person either. It also denotes that a person can only occupy one parking space. This relation need to have one entity nominated to become the dominant table and use programs or triggers to limit the number of related records stored inside the other table in the relation.

The Sub-type Cardinality is a 1:0 relationship and defined as having one optional side only. An example would be a person and programmer relation. This is a 1:0 relation meaning that a person can be a programmer but a programmer must always be a person. The mandatory side of the relation, in the case the programmer side, is dominant in the relationship. Triggers and programs are again used in the controlling the database.

The Physical Segment Cardinality is 1:1 relationship and it is demonstrated that both sides of the relationship are mandatory. Example may be a person and DNA patters. This relationship show that a person must only have one set of DNA patterns while the DNA patters as dictated by nature can only be applied on one person.

The Possession Cardinality is a 0:M relation (zero to many) relationship on both sides. For example, a person may own no phone or maybe plenty of phones but a phone may have no owner but has a potential to be owned by a person. In database implementation, a nullable foreign key column in the phone table is used to reference the person in its table.

The Child Cardinality is a 1:M mandatory relationship and is one of the most common relationships used most databases. An example would be a person table and membership table relationship. This relationship denotes that a person can be a member or not but a person can also be a member of many organizations. The foreign key in the membership table has to be mandatory and not null.

The Characteristic Cardinality is a 0:M relationship which is mandatory on both sides. An example would be a person and name table relationship. This denotes that a person should have at least one name but may also many names. The database implantation for this cardinality involves a nullable foreign key in the name table to the person table.

The Paradox Cardinality is 1:M relationship which is mandatory to one side. An example would be a person table and citizenship table relationship. The Paradox is similar to the Physical Cardinality. A person must have a citizenship and citizenship must have a person. But in this case, a person may have multiple citizenships.



Regards,

Ruchika Mandore  [ MCA ] 
Software Engineer
AeroSoft Corp

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Wednesday 29 February 2012

Relational database characteristics


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relational model



The use of keys

The relational model allows for the linking of data from different tables using keys. Using the Structured Query Language (SQL), linked data from multiple tables can be selected at once with so called JOIN queries. We will talk a lot more about keys later in this article.

Avoiding data redundancy

In a database design that adheres to the rules of the relational model, each data item, a username for example, is stored only once, that is, in one location. This avoids having to maintain the same data in multiple locations. The duplication of data is called data redundancy and this should be avoided in a good database design.

Constraining the input

Using a relational database you can specify what sort of data a database column is allowed to contain. You can create fields that contain numbers, decimal numbers, small texts, large texts, dates, etc.

Besides data types, database systems allow you to apply further constraints like length constraints and like enforcing the uniqueness of a certain field (username or email address for example) across all rows.

These constraints give you control over the integrity of your data. They prevent situations like

entering an address (text) in a field where you were expecting a number
entering a zip code of one hundred characters
ending up with two users with the same username
ending up with two users with the same email address
entering a weight (number) in a birthday (date) field
Maintaining data integrity

By setting field properties, by linking tables and by applying data integrity rules you can increase the reliability of your data.

Rights

Most relational database systems offer a rights structure with which rights can be assigned to different users. Some of the operations that can be allowed or disallowed to a user are SELECT, INSERT, DELETE, ALTER, CREATE, etc. These rights correspond to the operations that can be performed using the Structured Query Language (SQL).

Structured Query Language (SQL)

In order to actually perform operations on the database, like storing new data, and selecting and altering existing data, SQL queries are used. The Structured Query Language is relatively easy to understand and it allows advanced database operations, such as the selection of linked data from multiple tables with JOIN queries. As previously discussed, SQL is out of scope for this article. I will discuss SQL in a separate article. I will focus strictly on database design in this tutorial.

The way you design your database has a direct effect on the queries you need to write to retrieve data. That is another reason why it is good to think about how you design your database.




Regards,

Ruchika Mandore  [ MCA ] 
Software Engineer
AeroSoft Corp

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