Question

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Q1: Data Modelling is the primary step in the process of database design. Compare and contrast Conceptual data model versus Physical data model. Illustrates with help of example to list down data (entities), relationship among data and constraints on data.

Q2:What strategic competitive benefits do you see in a company’s use of extranets?

Answer 1

Ans.1) Data modelling is the first step in process of database design.The step is sometimes considered to be a high-level and abstract design phase, also refered to as conceptual design.

The aim of this phase is to describe:

The data contained in the database (e.g., entities: students, lecturers, courses, subjects)
The relationships between data items (e.g., students are supervised by lecturers; lecturers teach courses)
The constraints on data (e.g., student number has exactly eight digits; a subject has four or six units of credit only).

The relationships and the constraints are all expressed using the concepts provided by the high-level data model. Because these concmepts do not include the implementation details, the result of the data modelling process is a (semi) formal representation of the database structure. This result is quite easy to understand so it is used as reference to make sure that all the user’s requirements are met.

The third step is database design. During this step, we might have two sub-steps: one called database logical design, which defines a database in a data model of a specific DBMS, and another called database physical design, which defines the internal database storage structure, file organization or indexing techniques. These two sub-steps are database implementation and operations/user interfaces building steps.

In the database design phases, data are represented using a certain data model. The data model is a collection of concepts or notations for describing data, data relationships, data semantics and data constraints. Most data models also include a set of basic operations for manipulating data in the database.

Degrees of Data Abstraction

As any design starts at a high level and proceeds to an ever-increasing level of detail, so does database design. For example, when building a home, you start with how many bedrooms and bathrooms the home will have, whether it will be on one level or multiple levels, etc. The next step is to get an architect to design the home from a more structured perspective. This level gets more detailed with respect to actual room sizes, how the home will be wired, where the plumbing fixtures will be placed, etc. The last step is to hire a contractor to build the home. That’s looking at the design from a high level of abstraction to an increasing level of detail.

The database design is very much like that. It starts with users identifying the business rules; then the database designers and analysts create the database design; and then the database administrator implements the design using a DBMS.

Conceptual models

1. Provide flexible data-structuring capabilities

2. Present a “community view”: the logical structure of the entire database

3.Contain data stored in the database

• Show relationships among data including:
  • Constraints
  • Semantic information (e.g., business rules)
  • Security and integrity information
• Consider a database as a collection of entities (objects) of various kinds
• Are the basis for identification and high-level description of main data objects; they avoid details
• Are database independent regardless of the database you will be using.

Physical models

• Are the physical representation of the database
• Have the lowest level of abstractions
• Are how the data is stored; they deal with
  • Run-time performance
  • Storage utilization and compression
  • File organization and access methods
  • Data encryption
• Are the physical level – managed by the operating system (OS)
• Provide concepts that describe the details of how data are stored in the computer’s memory.

Ans.2)

An extranet can add value to your company by helping you communicate and collaborate more effectively with clients, customers, and partners. Particularly in the business-to-business market, an extranet can give your company an edge over the competition and save you money by streamlining traditional business functions and cutting overhead costs.

Extranets offer small businesses many other advantages:

Increased productivity. As you automate processes that were traditionally done manually, bottlenecks will disappear and your company’s productivity will increase. Critical information won’t get lost in the mail or buried in an e-mail inbox, and busy employees won’t miss or forget key events. An extranet can, for example, monitor business activities and trigger specific actions, such as automatically placing an order with a supplier when your inventory drops below a certain level.

Reduced margin of error. An extranet can reduce your margin of error, especially when you use it to give specific groups access to internal applications. This could involve something as simple as giving customers access to their order histories, or something as complex as processing orders from distributors and suppliers.

Flexibility. When you use an extranet to make information and applications available to partners, clients, and customers, everyone can operate when and where it’s most convenient. This self-serve approach frees you from unnecessary meetings and phone tag, and it cuts down on the costs associated with in-person information exchanges. For example, an extranet may allow you to provide customer-service information outside of regular business hours.

Timely and accurate information. On an extranet you can instantly change, edit, and update sensitive information such as price lists or inventory information. Compared to typical paper-based publishing processes, an extranet offers a unique opportunity to get hot information into the right hands before it cools — and before it’s out-of-date.

Shorter time to market. If your business is not moving at “Internet speed,” you risk being left behind. An extranet can help you get your products to market more quickly by making proposals and specifications available to suppliers, and giving clients and partners up-to-date information on current projects.

Reduced inventory. One of the hallmarks of a business-to-business extranet is its impact on supply-chain management. By linking your inventory system directly to a supplier, you can process orders as soon as the system knows you need them, thus reducing the stock you keep on hand and making the procurement process more efficient.

Build customer loyalty. Extranets make business easier for your customers. The more you make timely, accurate information available to your customers, the more likely it is you’ll keep their business.

As these examples demonstrate, an extranet can help you spend less on supplies, staffing, and other overhead costs. Given the investment an extranet requires, it may take time for savings to become apparent. Over a period of weeks or months, however, eliminating even one paper-based process can yield dramatic savings.