SQL Server Mentalist

Hi friends

Continuing from my last post on same series also we have completed following topics in my previous post as follows :

• BISQL # 72 – Laymen to SQL Developer # 3 – Assignment #1 – Part #2 – Why DBMS or What are Limitations of file processing systems « SQL Server Mentalist
• BISQL # 69–Laymen to SQL Developer # 1 – Introduction to brand New SQL Server Zero to Basics Series
• BISQL # 70 – Laymen to SQL Developer # 2 – Assignment #1 – Part #1–Introduction to Data and database Why Database exist ?

In this article we are covering following  points under Data Abstraction

What is Data Abstraction ?

What is Data Abstraction in Real World

Data Abstraction in Data Architect

How Data Abstraction works in DBMS ?

What are Levels of Data Abstraction

Physical level

Conceptual level / Logical Level

View level

The Need for Data Abstraction

Summery

We may find this concept difficult to digest but believe me this is just an information that we must know .. Even if you don not understand each of following topics then also its ok..

Now lets dig into Data Abstraction  ……….

Data Abstraction

What is Data Abstraction ?

The Data Abstraction layer is a software layer that helps to leverage the physical data, no matter how they are structured and provides integration of the data sources of interest. Many of the complexities involved in data services  by defining a Data Abstraction layer.

This can promote decoupling of information from data, ability to create virtually structured data, and creation of a central point to manage changes in data.

What is Data Abstraction in Real World

For example in real life whenever we are thinking of car we think of its various part and we never bother how each and every parts works together and we never want to learn that complexity also .

in a similar way in Database also we have various Data Abstraction where we will see how Data actually interact with layers of Physical and Logical abstraction

For the system to be usable, it must retrieve data efficiently. The need for efficiency has led designers to use complex data structures to represent data in the database.

Data Abstraction in Data Architect

In next Diagram we have shown exact place of Data Abstraction in Any Database Architecture 

How Data Abstraction works in DBMS ?

As shown in following diagrams interaction of External schema ,Logical Schema and Internal Schema.

Levels of Data Abstraction

1. Physical level
2. Conceptual level / Logical Level
3. View level

In next diagram we have shown relation between three levels of and shown exact use of each level with Database

Since many database-systems users are not computer trained, developers hide the complexity from users through several levels of abstraction, to simplify users’ interactions with the system.

One way of describing data abstraction could be in terms of the focal point of different levels.

Now lets discuss each level in various ways :

Physical level

Physical level emphasizes the "how" and "where" parts of the data storage. It will address mundane matters such as the data types, indexes and storage techniques like B-Tree, hashing and so on.

Physical level is lowest level of abstraction describes how the data are actually stored. The physical level describes complex low-level data structures in detail.

This also explain how actually data interact with system at physical level.

Conceptual level / Logical Level

At conceptual level, the emphasis lies on the "what" part of the picture. The content is stored along with the relationships tying scattered bits of data to each other, creating information.

This level has two names which are Conceptual level or Logical Level

The next-higher level of abstraction describes what data are stored in the database, and what relationships exist among those data.

The logical level thus describes the entire database in terms of a small number of relatively simple structures. Although implementation of the simple structures at the logical level may involve complex physical-level structures, the user of the logical level does not need to be aware of this complexity.

Database administrators, who must decide what information to keep in the database, use the logical level of abstraction.

View level

View level part may be considered the "who" part of the picture. This is an abstraction in the sense that filters can be applied to glean relevant information only; eliminating the unnecessary (or in many cases privileged) bits of data.

The highest level of abstraction describes only part of the entire database. Even though the logical level uses simpler structures, complexity remains because of the variety of information stored in a large database. Many users of the database system do not need all this information; instead, they need to access only a part of the database.

The view level of abstraction exists to simplify their interaction with the system. The system may provide many views for the same database.

All level when we combined together we have following view of Database just reference architecture:

The Need for Data Abstraction

Database abstraction is a powerful concept, and the idea behind this concept is that an application does not need to know anything about the structure of the databases where the data is stored. This allows us the following advantages:

• Portability

SOA services are independent of a specific database vendor. The services provide information obtained through ADSL without the knowledge of specific database technology being used, which makes it easier to replace one database technology with another from a different vendor.

• Flexibility

Ability to structure data so that the virtual structure can meet the requirements of new or existing SOA services.

• Homogeneity

Ability to provide single point integration to dozens of distributed data sources, structured or unstructured. This allows for integration of heterogeneous systems.

• Understandability

Ability to make data understandable by creating cohesive structure from diverse data sources.

• Application Decoupling

Ability to separate SOA services from the underlying physical data. The services make use of the data without specific knowledge of the databases.

Summery for data abstraction

Three levels of data abstraction are:
Physical level : how the data is stored physically and where it is stored in
database.
Logical level : what information or data is stored in the database (like what is the
data type or what is format of data.
View level : end users work on view level. if any amendment is made it can be
saved by other name.
for the database to be usable it must retrieve data efficiently .this efficiency led designer to use complex data structure in the database

Hope this Helps !!!!

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