2. The three-level (or three-tier) system architecture can be interpreted in different ways. Describe, using a well-annotated diagrams, the different and distinct meanings of the phrase three-level architecture for the following system architecture Databases and the ANSI-SPARC architecture. [5] b) Many organisations have a choice to deploy their data resources and services EITHER using their own IT infrastructure, OR by choosing to have their data resources and services managed remotely by hosting databases on the ‘Cloud’. Discuss the key strengths and limitations of these alternative approaches. [15]
Answers
Internal Level/Schema
The internal schema defines the physical storage structure of the database. The internal schema is a very low-level representation of the entire database. It contains multiple occurrences of multiple types of internal record. In the ANSI term, it is also called "stored record'.
Facts about Internal schema:
The internal schema is the lowest level of data abstraction
It helps you to keeps information about the actual representation of the entire database. Like the actual storage of the data on the disk in the form of records
The internal view tells us what data is stored in the database and how
It never deals with the physical devices. Instead, internal schema views a physical device as a collection of physical pages
Conceptual Schema/Level
The conceptual schema describes the Database structure of the whole database for the community of users. This schema hides information about the physical storage structures and focuses on describing data types, entities, relationships, etc.
Three-level (or three-tier) system architecture
Explanation:
Three levels in DBMS:
1.External level (View level) :
This level describes that Part of database that is relevant to each user
2.Conceptual level(logical level):
It describes what type of data is stored in database and relationships among the data
EX:entities,attributes,constraints on the data and their relationships
It also decribes about integrity and security of data
3.Intenal lever(storage level):
It is physical representation of database
It describes how the data is stored and also it covers the data structures and file organisations
We can maintain DBMS in single tier and multi tier
n-tier architecture means same in functionality but independent in modules
DBMS architecture helps in design, development, implementation, and maintenance of a database. A database stores critical information for a business or an organisation or any university….
Choosing the correct Database Architecture helps in quick and secure access to this data.
There are 3 types of DBMS architectures:
1)1-tier architecture:
Rather than database cloud server we use local file server.
In 1-tier architecture the server,the client and the database resides on the present worling system.That is there is no cloud databases,servers on clouds.
Generally we practice SQL in our system during learning by installing Oracle database(for example any databse like Mysql,Nosql) and learn writing queries for the databases that are being resided in our system.
The very simple of database architectures is 1-tier architectures
In cases where there is no frequent change of data we use 1-tier architecture
2-tier Architecture(client-serrver architecture) :
We have client systems interact with cloud databse servers instead of file servers
In 2-tier architecture all the server and clients are resided in our system but the data is being stored in cloud.We manipulate data using the server and clients but the data gets manipulated in the database in cloud.
Most of the DBMS offers ODBC drivers for their DBMS. 2 tier architecture provides added security to the DBMS as it is not exposed to the end user directly.
Two tier architecture gives direct communication so its fast.
3-tier architecture:
It depends on networking information to access the clouds
The three tires are:
1.Client tires
2.Logic tire(application servers)
3.database tier
It seperates tiers from eachother based on complexicity of the users and how the used present upon database
In database tier the data along with the query processing is present
In application tier an abstract view of database and acts as mediator between the user and database
The Client tier(presentation) the end user operate
It contains presentation layer,application layer and databse server
The application layer present between the user(presentationlayer) and the database server
So any user requests will be implemented on databse server through application layer.
The application layer(business logic layer) also processes functional logic, constraint, and rules before passing data to the user or down to the DBMS
It supports data independence that is we can access the data from same databases at a time using two or more client requests.