DBMS NOTES UNIT 2

                                           DBMS NOTES

UNIT 2

Database System Architecture 

Three-level architecture or ANSI/SPARC architecture are other names for the three-schema design.
A specific database system's structure is described using this approach.
The physical database and user apps are kept apart using the three schema architecture.

There are three levels in the three schema architecture. The database is divided into three sections by it. 

Three Schema Architecture's Goals

Three-level architecture's primary goal is to save the underlying data just once while allowing multiple users to access the same data in a personalised view. It does this by dividing the database's physical structure from the user's perspective. The following justifies the desire for this separation:

Different views of the same data are required for different users.

Over time, the method by which a certain user needs to view the data may vary.

Users of the database shouldn't be concerned about the internal operations and physical implementation of the system, including hashing, internal structure optimisation, data compression and encryption methods, etc.

The same data should be accessible to all users based on their needs.

Three Architecture Levels:

The external level of abstraction, which is the highest, addresses how consumers interpret the data. It consists of many external schemas or user views, each customised to meet the requirements of distinct user groups.

Conceptual Level: Often referred to as the logical level, it serves as a user community's representation of the complete database. The conceptual schema, which outlines the limitations and organisation of the data kept in the database, is included in it.

The internal level of abstraction specifies the physical storage of data in a database system. It is the lowest level of abstraction. It contains the internal schema, which describes the database system's actual physical storage configurations and access techniques. 

What is DBMS schema ?
In this context, database design refers to the DBMS schema. Let's use the employee table as an example, for instance. The following characteristics are present in the employee table. EMP_ID, EMP_ADDRESS, EMP_NAME, and EMP_CONTACT are these characteristics. These represent the employee table's schema.

Three extra categories are applied to schemas. These three are listed in order.

PHYSICAL schema.

LOGICAL schema.
VIEW schema.
The database's logical perspective is specified in the schema. It offers some information about the database and the locations of the necessary data.

1. Physical schema: The database is designed at the physical level in the physical schema. The schema at this level explains the management of the storage and the storage of the data block.

2. Logical schema: The database is logically designed in the logical schema. The programmer and data administrator carry out their duties at this level. Additionally, certain data is organised and saved at this level. However, for the suggested security, the internal implementation data are concealed in the physical layer.

3. View schema: The database is created at the view level using view schema. The way users interact with the database system is described in this schema.

What is instance in DBMS?

A database management system (DBMS) instance is a collection of data that is kept for a specific period of time. The characteristics of the database within the specific DBMS are specified by the database schema. An instance of the database management system is defined as the value of a specific attribute at a given point in time.

For instance, we used the attribute of the schema as an example in the example above. Each table in this example has two rows, or two records. The employee table has some instances in the database's schema above because the table has some instances of all the data.

What is Data Independence in DBMS?

1. Logical Data Independence: Logical data independence refers to the ability to change the conceptual schema without having to change the external schemas or application programs. It allows modifications to the database structure without affecting the way users access the data.

2. Physical Data Independence: Physical data independence refers to the ability to change the internal schema without affecting the conceptual or external schemas. It allows modifications to the physical storage structures and access methods without impacting the logical structure of the database.

Classification of Database Management System:

1. Centralized DBMS: In a centralized DBMS architecture, all data is stored and managed in a single location. Users access the database through a single interface, and all data processing tasks are performed centrally.

2. Client-Server Architecture: In a client-server architecture, the database is stored on a server, and clients communicate with the server to access and manipulate the data. This architecture allows for distributed processing and scalability, as multiple clients can access the database simultaneously.

Types of Client Server Architecture :

1 tier architecture

The presentation, application, and data administration layers are all closely linked into a single system in a one-tier architecture. Small-scale applications where all processing is done on a single machine are the main uses for this architecture.

+------------------------------------+ | Application | | Layer | +------------------------------------+ | Presentation | | Layer | +------------------------------------+ | Data Management | | Layer | +------------------------------------+

2 tier architecture

The application logic in a 2-tier architecture is divided between a client and a server. While the server is in charge of data management and business logic, the client is in charge of the presentation layer and user interaction.The application logic in a 2-tier architecture is divided between a client and a server. While the server is in charge of data management and business logic, the client is in charge of the presentation layer and user interaction.

+------------------------------------+ | Application | | Layer | +------------------------------------+ | Presentation | <----- Client Machine | Layer | +------------------------------------+ | Data Management | <----- Server Machine | Layer | +------------------------------------+

3 tier architecture

The display, application, and data management layers comprise the three divisions of the application logic in a three-tier architecture. Compared to a 2-tier architecture, this one offers greater flexibility and scalability.

+------------------------------------+

|           Application              |

|              Layer                 |

+------------------------------------+

|             Presentation           |      <----- Client Machine

|                Layer               |

+------------------------------------+

|            Business Logic          |      <----- Application Server

|                Layer               |

+------------------------------------+

|          Data Management           |      <----- Database Server

|                Layer               |

+------------------------------------+

what are Data Models? Explain each  Records- based Data Models, Object-based Data Models, Physical Data Models and Conceptual Modeling.

 Conceptual Data Model

The conceptual data model is helpful in understanding the needs and requirements of the database since it provides a high-level description of the database. This approach is employed during the requirement-gathering phase, which is to say, prior to the Database Designers beginning to create a specific database. The entity/relationship model (ER model) is one such well-liked model. Entities, relationships, and even properties that are utilised by database designers are the focus of the E/R model. With regard to this idea, stakeholders and users who are not technical or who do not understand computer science can nevertheless have a conversation and have their needs recognised.

A high-level data model called the Entity-Relationship Model (ER Model) is used to specify the data and the relationships between them. It is essentially a conceptual design for any database that makes creating a data view simple.

Elements of the ER Model:

Real-world objects are referred to as entities. It could be a class, name, location, or item. In an ER Diagram, these are shown by a rectangle.
Attributes: An entity's description is referred to as an attribute. In an ER Diagram, these are represented by an ellipse. For a student, it could be their age, roll number, or marks.
Relationship: Relationships are what establish the connections between various entities. Relationships are represented by rhombuses and diamonds.

OBJECT BASED DATA MODEL 

 In object-based data models, the representation of data is the main concern. The data is separated into a number of entities, each with certain distinguishing features. Furthermore, there exist certain links between these data elements.

Accordingly, the entities in object-based data models are based on real-world models and how the data is really used. The way the data is visualised and integrated is more important than the actual content of the data.

A few instances of object-oriented data models include

 Entity Relationship Data Model

Real-world circumstances are represented as entities in the ER model. In the ER diagram, these entities' characteristics represent their properties, and relationships represent the links between them.

In data designing, an ER model is typically seen as a top-down method.

  

Model of Object-Oriented Data

Object-Oriented Data Model

Using real-world scenarios is also the foundation of object-oriented data models. The scenarios are represented as objects in this model. Objects with comparable functionalities are connected to one another and grouped together.

Here's an illustration of an object-oriented data model:

In this paradigm, there are two objects: PERSON and EMPLOYEE.
Name, address, phone number, and age are properties of PERSON.
The attributes Employee ID, Employee Type, and Department ID are present in EMPLOYEE.

Records- based Data Models

Record-Based Data Model: This type of data model is used when a database is set up with several records in a fixed format. Every record type has a set amount of fields or characteristics, and each field typically has a set length.

Additionally, it is divided into three categories:

Hierarchical Data Model: A group of records serves as the model data's representation in a hierarchical data type. Links in this indicate the relationships between the data. A tree data structure is employed in this concept.
IBM created it in the 1960s to handle massive volumes of data for intricate manufacturing operations. An inverted "tree" represents the fundamental logical structure of a hierarchical data model.

Network Data Model: A group of records serves as the model data representation for networks. Links in this indicate the relationships between the data. In this model, graph data structures are employed. It allows for the existence of several parents on a record.
Take social media platforms like Facebook, Instagram, and so forth.

Relational Data Model: The data and their relationships are represented by tables in the relational data model. Every table has a number of columns, and each one has a distinct name. This model is basic.

 Physical Data Model

It's now time to put a logical model into practice by integrating it into an actual database.

As part of the physical data model, there should be:

A certain DBMS (like Couchbase, for example)
The method(s) used to store data (RAM, disc, hybrid, etc. To combine the speed of RAM with the durability of disc, Couchbase comes with an integrated cache.
Methods for allowing divisions, shards, replications, etc. Partitioning and sharding for Couchbase are automatic processes. A drop-down box for replication allows you to choose the desired number of replicas.
DBAs and/or developers usually construct the physical data model.As part of the physical data model, there should be:

A certain DBMS (like Couchbase, for example)
The method(s) used to store data (RAM, disc, hybrid, etc. To combine the speed of RAM with the durability of disc, Couchbase comes with an integrated cache.