What is 3-tier architecture of DBMS?
Database models?
What is database schema?
What is database instance and data independence?
What is 3- tier architecture in DBMS
The design of a database management system rely on it's architecture. It can be centralized or decentralized or hierarchical. The architecture of a Database management system can be seen as either single tier or multiple tier. An n-tier architecture divides the whole system into related but independent n modules, which can be freely modified (change), altered, or replaced.
3-tier architecture - A 3-tier architecture segregate it's tier from each other based on the complexity of the users and how they use the data present in the database. 3-tier architecture is the most universally used architecture to design a database management system(DBMS) .
There are three tier in 3- tier architecture.
- Database tier - we can simple call it data tier because the database live in along with it's query processing languages.
- Application tier - This tier is also called as middle tier, the application layer sits in the middle and behave as a mediator between the end -user and database. This application tier introduce an abstract view of the database for the users. The database tier also called as data tier is not informed of any existence of the database beyond the application.
- Presentation tier - we can simple call it user tier because in this tier the end-users operate(perform their all operations). The user's are not aware of anything about another tier of the database beyond this layer. At the presentation tier or user tier, multiple view means different different views of database can be provided by the application .All the views are created by applications that reside in the application tier.
What is data models
Data models explain how data is attach to each other and how they processed and stored inside the system. Data models describe how the logical design of a database is modeled. Data models are fundamental entities to introduce abstraction in a database management system(DBMS). Initially, data models were not so systematic for this reason they were subject to introduce lot's of duplication and update anomalies(inconsistency).
Entity-relationship model
First of all we have to learn about the entity and relationship means
Entity - An entity is a real-world object that can be easily identifiable(it can be anything, either alive(animate) or not alive (inanimate) ) having properties called attributes(Features). Each and every attribute is describe by it's set of values called domain. For example- in a university database, a student is view as an entity. Student has numerous attributes like name, roll number, age, mobile number,class, etc.
Relationship - The logical connection among entities is called relationship. Relationships are mapped with entities in numerous ways. Mapping Cardinalities describe the number of association between two entities:
Mapping Cardinalities
- one to one
- one to many
- many to many
- many to one
Entity-relationship also known as ER model is based on the concept of real- world entities and relationship among them. The entity-relationship model creates entity set, relationship set, general attributes and constraints.
ER model is suitable used for the conceptual design of the database. ER model is based on-
- Entities and their attributes
- .Relationship among entities
Relational Model
The most popular data model in database management system is the relational model. In the relational model data is stored in tables called relations. Each row in a relation contains a unique value. Each column in a relation hold values from a same domain. Relational model is more systematic and scientific model than other's model.
what is database schema
A database schema is describe as blue print. Database schema is the skeleton structure that be regarded as the logical aspect (view) of the whole database. Database schema describes how the data is organized and the relation among them are connected. It put together all the constraints that are to be applied on the data.
A database schema describes its entities and the relationship among them. Database schema contain a descriptive characteristic of the database. It's the database designers who design the schema to help programmers to understand the database and make it useful for them.
The database schema can be divided into two categories-
- Physical database schema - Physical database schema be relevant to the authentic storage of data and it's form of storage like indices, files, etc. Physical database defines how the data will be stored in a secondary storage.
- Logical database schema - Logical database schema describes all the logical constraints that require to be applied on the data stored. It describes tables, view, and integrity constraints.
what is database instance and data independence
As we discussed about database schema, which is also called blue print or skeleton structure of the database. Database schema is designed when the database doesn't exist at all. A database schema doesn't hold any data or information as soon as database is operational, it's very tough to make any changes to it. A database instance is a situation of operational database with data at any given time it hold a snapshot of the database. Database instances be liable to change with time. A DBMS( database management system) make sure each and every instance means state is in a valid state, by following all the validations, constraints, and conditions that the database designers have imposed.
As we know database systems are designed in multi-layers ..if a database system is not multi-layered, then it becomes very tough to make any changes in the database system.
Data independence - A database system holds a lot of data. Database system stores data about data, know as metadata, to find and retrieve data effortlessly. It's very tough to change and modify or update a set of metadata once it is stored in the database. But DBMS become larger , it needs to change over time to satisfy the demands of the users. If the whole data is dependent, it would become a very tough and highly complex work.
Metadata follows a Layered architecture, so that when we change data at one layer , it doesn't have an effect on another level. This data is independent but mapped to each other.
There are two type of data independence
- Logical data independence - It is data about the database, like how it stores information about how data is managed inside.
- Physical data independence - Physical data independence is the ability to change the physical data without impacting the schema or logical data.
Conclusion
As for future aspects relational database model will more used universally because it's one of the most popular and scientific model.