Data+modeling II

=Data Modeling II: Entity-Relationship Modeling= Tuesday, October 27, 2009

Topic overview:
Data Modeling is the process of precisely describing the data requirements for an information system (or set of information systems) and how the different data elements interact with each other. In class today we will build on Sunday's discussion of the Relational Data Model by introducing Entity-Relationship (ER) Modeling. As we discussed in class on Sunday, ER modeling is a more abstract way of describing and organizing a set of data elements than relational modeling. Relational models map in a direct and obvious way to the structure of a relational database. ER models, on the other hand, describe data elements, their attributes, and the relationship between the data elements independent of a specific type of database. That is, a data model described with an ER diagram can generally be implemented with a relational, object-oriented, or other type of database.

By the end of today's class you should be able to:
 * Explain the difference between an //Entity//, an //Attribute//, and a //Relationship// in an Entity-Relationship Model
 * Use basic ER modeling constructs to model simple data elements, events, and transactions
 * Explain the different roles that ER modeling and Relational modeling play

**Preparation for class:** There is no new reading for class today though I encourage you to review the slides on ER modeling from Sunday's talk prior to today's class.

I have also posted a book chapter on ER modeling in the Course Documents section of Blackboard. To comply with copyright law (fair-use for educational purposes), I need to post the chapter to Blackboard, where you can only download it after you have authenticated as a Carnegie Mellon student. I will not quiz you on the ER modeling chapter in class but you will likely find it very helpful in completing Assignment #3.

**Reference materials:**
Slides:

**Student questions:** As usual, in preparation for today's class, you need to provide at least one thoughtful question raised by your reading of the material you have been asked to prepare for class today. These questions should be posted at least 4 hours prior to the beginning of lecture.

[Bob Monroe] Would you use both an Entity-Relationship model and a Relational model on a single IS project? Do you need to pick one or the other? If you use both, do you use one before using the other, or do you use them at the same time?

[Fatima Hilal] The definition of entity states that, entity is a person, place, object, event, concept in the user environment about which the organization wishes to maintain data. However, when identifying entities we find that it should not be a user of the database system and not an output of that database system, so what are the reasons behind this?

[Noora Al-Mannai] Which type of the relationship types is mostly used the Unary Relationship, the Binary Relationship, or the Ternary Relationship? When do we need to use relationship types of larger than 3 entities?

[Abdulla Ali Al-Kuwari] When modeling tables for the information needed in an IS system, the more precise the tables the better the modeling is (in other words, try to minimize your columns to reduce redundancy). However, this will make too many tables when the IS system is very large which will decrease the performance of system. How can the company decide the degree of preciseness it needs while trying to minimize the pressure on the servers?

[Benazir Anis] If Firm A has a greater number of entities in comparison to Firm B. Does this mean that Firm A is better off? Or do attributes of entities play a larger role in determining the success of a firm?

[Hadi Murtada] To have a better system for the future, managers work on having it more complex thus spending more time in creating the system in the beginning and less time searching the database in the future. How much is complexity beneficial?

[Hadi Murtada] Don't you think for small companies having a simple database will cost less and take less time? thus there is no use for complex systems.

[Omnia Khalid]: Based on what do managers make the decision of using either Entity-Relationship model and a Relational model?

[Eatidal Al-Qatami] What is the main difference between ER models and Relational models? What are the differences between identifiers in ER models and keys in the Relational model?

[Shuaa] How important is identifying the entity type to the quality of information ?

[Yara Saeed] For a large complicated data base, is adpoting relational data base modelling worth it in terms of the extra time it take to answer a query?

[Mathew James] How do organizations actually measure the quality of information or data in an information system (or set of information systems) ?

[Maryam Al-Kuwari] : an integration allows separate systems to communicate directly with each other and there are two types of integration, forward and backward, what is the difference between them? and which one has a a larger effect on the organization's database?

[Omar El-Zoheery] Is Data mining, if affordable appropriate for companies that have not yet become of a big significant size? since extracting useful information from the raw data can allow improvements and change in processes to benefit the company.

[Jummana Kahlout] When is the relational model used? How do you decide whether you should use the relational model or the Entity-Relationship model?

[Samira Islam] How is the accuracy of data maintained in a typical data warehouse?

[Mohammed Al-Thani] To what extent does the five common characteristics of quality information can be a threat for a company that maintains low quality information?

[Ramsey Massouh] Many organizations use data mining, where they analyze the raw data they have into more useful ones. What is possible example for an organization that uses this process?

[Maryam Alsemaitt] Is the information data base able to automatically make business decisions ? and how helpful/harmful could that be if it happens ? [Nada Al-Mahmeed] there is two types customer information integration: backward and forward. What factors must a company consider to help them decide with is best to use?