Database System Environment

DB systems refers to an organization of components that define and regulate thr collection, storage, management and use of data. The components of a DB system are:

1. hardware
2. software
3. people
4. procedures
5. data

Hardware

• Identifies all the systems physical devices. includes computers, computer peripherals(like printers, scanners, etc), network components, etc.

Software

• Its the collection of programs used within the DB system. It includes the OS, DBMS, and other programs.
  • OS, manages the hardware resources and provides an environment for the execution of programs.
  • DBMS, manages the DB and provides an environment for the execution of DB applications.
  • Application programs, are programs that use the DBMS to access and manipulate data and to manage the operating environment of the DB.

People

• Includes all users associated with the DB system. They are the ones who use the DB system to perform their tasks.

• Five types of users:(there are many more)

  • System administrators, oversees the DB system general operations.
  • Data modelers(architects), designs the DB structure based on the requirements of the organization.
  • DB administrators, physically implement the DB according to the logical design and maintain the DB.
  • System analysts and programmers, develop the application programs that use the DB.
  • End users, use the DB system to perform their tasks. e.g in a banking system, the end users are the customers.

Procedures

• Are instructions and business rules that govern the design and use of the DB system.
• Procedures enforce the standerds by which business is conducted within the organization and with customers.

Data

• Data are the collection of raw facts stored in the database.

• To enter appropriate data into the database and how such data are to be organized is a vital part of the database designer’s job.​

ANSI-SPARC architecture

• Its an abstract design standard for a DBMS first proposed 1975.
• Most modren commercial DBMSs are based on this system. however, it never became an formal industry standard.

It consists of 3 layers:

1. External level, how data is viewed by an individual user.(viewed based on the user’s needs, e.g shanging an attribute name aka aliasing)
2. Conceptual level, how data is viewed by A community of users.(original data)
3. Internal level, how data is physically stored.

• The whole point of this architecture is to ensure data independence, that means if one layer is changed, the other layers are not affected.

Objectives of the architecture:

• allow all users to access the same data.
• make sure a users view is immune(meaning unaffected) to changes made by other users.
• allow DBA (database administrator) to change the conceptual/internal level without affecting the external level.
• ensure the internal structure is unaffected by changes to the physical aspects of the storage.
• users can use the DB without needing to know the physical storage details.

Again, all these objectives are required to achieve data independence.

• Logical data independence, conceptual schema changes should not require changes to the external schema.
• Physical data independence, internal schema changes should not require changes to the conceptual schema.

Database architecture

ANSI-SPARC architecture is a conceptual model of a DBMS. It does not specify how the DB is physically implemented. The physical implementation is called the DB architecture.

a few database system architectures that are presently in use:

• Traditional mainframe architecture
• Personal computer - stand-alone architecture
• File sharing architecture
• Two-tier client/server architecture
• Three-tier client/server architecture

Database architectures can be distinguished by examinig the application logic is distributed throught the system. Application logic has 3 components:

• Presentation logic, how the data is presented to the user.
• Processing logic, handles data processing logic, business rules logic , anddata management logic.
• Storage logic, resposible for storage and retrieval of data from actual storage devices.

… the type of architecture is determined based on where these components are processed.

Traditional mainframe architecture

• earliest implementation of DB approach.
• mainly used by large organizations to store and process large amounts of data.
• from the name, DB resides on a mainframe computer.
• Applications are run on the same mainframe computer via different terminals.

Personal computer - stand-alone architecture

• DB resides on a PC(hard disk).
• Applications run on the same PC and directly access the DB. in such case the application is technically the DBMS.
• business rules are enforced in the application running on the PC.
• A single user can access the DB application.

File sharing architecture

• PCs are connected to a LAN (local area network) and share a common file system.
• A single file server stores a single copy of the DB files.
• Applications run on each PC on the LAN and access the same set of files on the file server. The application is also the DBMS.
• Business rules are enforced in the applications - Also, the applications must handle concurrency(Concurrency refers to the ability of a system to allow multiple users or processes to access shared resources, such as data or files, at the same time.) control. Possibly by file locking.
• Each user runs a copy of the same application and accesses the same files.

Two-tier client/server architecture

• A Two-tier Architecture in DBMS is a Database architecture where the presentation layer runs on a client (PC, Mobile, Tablet, etc.), and data is stored on a server called the second tier.
• provides added security to the DBMS as it is not exposed to the end-user directly.
• A Contact Management System created using ​ MS- Access is an example of Two-tier architecture.

Three-tier client/server architecture

• A Three-Tier Architecture in DBMS is the most popular client server architecture in DBMS in which the development and maintenance of functional processes, logic, data access, data storage, and user interface is done independently as separate modules.

• The three tiers are:

  • Presentation layer, runs on the client and is responsible for presenting data to the user (PC, Mobile, Tablet, etc.).
  • Application layer, runs on the server and is responsible for processing the data and providing the results to the presentation layer.
  • Database.

any large wibsites on the internet are built using this architecture.

Qs?

• Define the terms data and information. Explain how the two terms differ.​

Data is a collection of raw facts. Information is data that has been processed to be meaningful and useful.

• Compare and contrast the two-tier client server architecture for traditional DBMSs with the three-tier client server architecture. Why is three-tier architecture more appropriate for the Web?​

Two-tier client-server architecture is a traditional architecture that consists of two layers: the client layer and the server layer. In this architecture, the client application directly communicates with the database server. The client layer provides the user interface and the application logic, while the server layer provides the database management system and the data storage.

Three-tier client-server architecture, on the other hand, is an architecture that consists of three layers: the presentation layer, the application layer, and the data layer. In this architecture, the client layer communicates with the application server, which in turn communicates with the database server. The presentation layer provides the user interface, the application layer provides the application logic, and the data layer provides the data storage and management.

The main difference between the two architectures is that in the three-tier architecture, there is an additional layer between the client and the database server. The application server acts as an intermediary between the client and the database server, providing additional functionality such as application logic, data validation, and security.

The three-tier architecture is more appropriate for the Web because it provides better scalability, reliability, and flexibility compared to the two-tier architecture. The application server in the three-tier architecture allows for load balancing and horizontal scaling, which can help to handle large numbers of concurrent users. Additionally, the three-tier architecture separates the application logic from the data storage, making it easier to modify and upgrade the application without affecting the data storage. This makes it easier to adapt to changing business needs and user requirements.

Furthermore, the three-tier architecture also provides improved security, as the application server can act as a firewall, protecting the database server from direct access by the client. This helps to prevent unauthorized access and improves data privacy.

Overall, the three-tier architecture is more suitable for Web applications, as it provides better scalability, reliability, and security, and enables more flexibility in application development and maintenance.

• Discuss the concept of data independence and explain its importance in a database environment.

Data independence refers to the ability to change the database schema without affecting the applications that use the data. There are two types of data independence: logical data independence and physical data independence.