DITA: Database Technologies

Good Evening everyone,

This post is going to be the last as it concerns the Data Information and Technology Architectures coursework.

In the previous post we focused a lot on the method of storing and representing data in computers by using files. But except from this widely known method there is also another one which is more efficient and this is the database approach method. So in this post I am gone mention some characteristics of the database approach method and then I am going to focus on the relational database model and the technologies to retrieve data.

It was the disadvantages of the file approach that pushed the data processing departments of the organisations to find a new method to store and manage large amounts of data. The main disadvantage of the file approach method is the dependence that exists between the data and the programs. Moreover because the data are stored in separate and unrelated files that might even have different format, takes longer to access and retrieve them and often is likely to have data that are being duplicated. These duplicate data except from the fact that capture more space they can also cause problems when it needs to be updated or needs to be retrieved.

On the other hand the database approach is completely different and at the same time much more efficient. The fact that the database approach has a lot more advantages and is more effective from than the file approach is result of the way that the data are being stored and organised.

All data are being gathered in a central and corporate database according to the relationships that might exist between them. There is a Database Management System, also known and as DBMS, that centrally manages all the data in the database. Because of this gathering of the data and also because of the central way that the DBMS manages them is being avoided the appearance of duplicate information. With no duplications, we avoid possible inconsistencies in the data which has as a result the system to be more integral.

The DBMS as we mentioned and to the lecture is a complex piece of software, which acts as the interface between the users and the data. So the information that the data contain is shared between the users that require it and the DBMS allows the users to retrieve only the information that is being related to them. Moreover with the DBMS the security is better from the file method approach, as it concerns accessing the data, because not everyone is allowed to access them. The database has an administrator known as Database Administrator, who allows to users to access or not the data. But the most important thing with the database approach is that the data are independent, so when changes need to be made to the database's applications and mechanisms these changes doesn't affect the data.

In the relational model the data of an application are being represented as a group of relations between the data. In our case the application is a whole database so the relational database is being represented as a collection of two-dimensional tables which is the most common and practical way to express the relations. In order to make this representation more comprehensive we have an example. In the table that follows every row is known as a record and it refers to a unique student.

All these records are composed by a set of attributes which take specific values. These set of attributes in every relational database are composed in a way that we won't have any duplicates. The SSN attribute is an attribute that takes a unique value for each student, so if we know this number we can find any student that we are looking for, this kind of attribute is known as primary key. Every relation has a primary key but in some cases this key might be consisted of more than one attributes (composite foreign key). Apart from the primary key in some relations we might also have foreign keys. These keys are references to other tables. This means that there are relationships that exist between different tables.

But in order to create these tables, which means to start designing the relational database, the best thing that we should do first is to create a diagram known as entity-relationship (ER) diagram for our database. With this type of diagram as we can realize from its name we capture the entities of the database which are the tables/relations that we have already mentioned. But with the diagram we also find the relationships that might exist between the entities. Once we have implemented the ER diagram then we can create our tables in the two-dimensional form, that we have mentioned, and as a result we can create the whole relational database.

The SQL initials stand for Structured Query Language which is the most widely language that is being used to manage Database Management Systems. With the SQL we can create the tables that we have mentioned in a way that the computer systems can understand what they represent. Moreover after having implemented all the tables of the database that the DBMS manages users of the database can use SQL expressions in order to retrieve data that might need, update data that already exist or even add/delete data.

Here I have some examples of how you can create a table in SQL, how you can insert records to this table and of course how you can retrieve data from this kind of tables.

This is an example of how we can create the table of our example

Here is an example of how we can add a record to the table that we have created

With similar way can add as many records to the table as we want

And finally here is an example of how we can retrieve specific data from a table like the one that we have created

In this example we retrieve the values for the Name and the SSN attributes from all Students that exist in our table with the GPA's attribute value being more than 3.5

In conclusion we must say that the database approach has been very useful not only in the computer society but also to everyone that has to do with large amounts of data. The database approach has provided a much more efficient way to organise, store and manage data. This in combination with the relational model and the technologies that "escort" it, it has given to everyone an even more fast and effective way to retrieve data that are important to them.

REFERENCES

1. Andy MacFarlane, Richard Butterworth (2009), "Digital Information Technologies and Architectures", Lecture 7: Structuring and querying information stored in databases, City University.
2. Andy MacFarlane, Jonathan Raper and Jason Dykes (2009), "Information Technologies and Architectures", Lecture 8: Information Retrieval, City University.
3. http://whatis.techtarget.com/
4. http://aetos.it.teithe.gr/~amarg/Databases/Chapter03.pdf
5. http://sqlcourse.com/