Entity Relationship

Disecting Relationships {5}

by Kevin S
It’s becoming clear that Entity-Relationship models can be just as complicated as Human-Relationships. Fortunately, the journal “Improving Database Design through the Analysis of Relationships” is here to shine some light on the subject. This journal quickly covers all of the basics and dives into a detailed study of relationships. They cover such sticky situations which are often not divulged deeply in textbooks such as high degree relationships, derived relationships, and several more. The four aspects they use as a guide to analyzing a relationship are as follows: read more...

Introducing UML {2}

by Rudy P
The article i read this week was “Conceptual Data Modeling in the Introductory Database Course: Is it Time for UML?” by James Suleiman and Monica Garfield. This article gave a few reasons why the Unified Modeling Language or UML should be taught in introductory database courses at universities. When teaching conceptual data modeling, a majority of  schools teach the Entity Relationship or ER notation. This is for various reasons including preference and text book support, as many text books only dedicated only a single chapter or a part of the appendix to UML. There have been an increase in the teaching of UML in courses, however not as the primary modeling notation. The main fact backing the claim that UML should be taught in introduction to database course is its use in industry. The authors make the claim that UML has become an increasingly popular notation in the workforce, and thus should be taught in a more detailed manner in academia. read more...

The Temporal Attribute {Comments Off on The Temporal Attribute}

by Joshua L
This article that I chose went over the introduction of a temporal extension to the EER model and the query language GORDAS. The authors introduced the idea of lifespan to an entity by using a temporal element. Temporal attribute values were defined to be functions from the time domain to the attribute domain of an entity. They then presented the concepts of temporal selection conditions and temporal projections. Temporal selection conditions can be used to select entities from an entity set based on their temporal properties. Temporal projections are used to project the attributes of selected entities over a certain time interval for display. The authors also discuss temporal aggregation functions, which are statistically independent to the regular types of aggregation functions used in non-temporal data models. read more...

The differences of UML and ER model {3}

by Polun L
The article, “How to Draw an Architectural Data Model in UML”, by David C. Hay, talks about the differences of UML model and ER model. At the beginning of the article, the author described the development of entity/relationship data model which was formalized in 1970’s. Two decades later, the Unified Modeling Language (UML) was officially released. However, programmers found out that UML model is very different from ER model because they have significantly different structure in relational database. Even though object oriented programmers attempted to save persistent object data in relational database, it still could not make UML and ER model to be consistent. Finally, programmers realized that UML was developed to support object oriented design while entity relationship modeling was designed to support the analysis of business structures. In the end of the article, the author listed a guideline for those who would like to draw a ER model using  a  UML diagramming tool. read more...

Basics of An ER Diagram {Comments Off on Basics of An ER Diagram}

by Jamal A
The article I read talks about how important it is to create an ER Diagram, and how it should be
the starting point for software development projects. According to the article, “The very first step to
create an ER Diagram is to identify the nouns (entities)”.  For example: Company, Employee, and Project.
The article explained how ER Diagram “transmits a lot of information with a very short notation”.
There are some important signs to remember when creating an ER Diagram, For example:
Zero through Many (crow’s feet, O), One through Many (crow’s feet, dash), One and Only
One (dash, dash), Zero or One (dash, O). These are some of the symbols used when creating an ER Diagram.
The article also over viewed the three relationship types and explained how they are used.
These are: One to Many, Many to Many, and One to One. It went in further detail about these relationships
and explained which the most common relationship types are. read more...

The Importance of Learning to Identify Relationships and Entities. {1}

by Kevin Q
The peer-reviewed journal I read discussed reasons that students have trouble grasping and learning data modeling. The main reason being that students have a hard time identifying the relationships among the entities, and not so much in how to express the relationships. Students who do not learn how to identify relationships and thus create them in their data models will eventually run into problems due to poor data modeling.Typical mistakes that Dr. Watson has seen in his years of teaching include: “Not recognizing that an attribute is an entity, failing to generalize several entities as a single entity, not reading relationships both ways, and ignoring exception that result in a failure to represent reality.” Students who are good at identifying relationships are better off than student who can create diagram representations but unfortunately cannot interpret the relationships and entities. Watson then goes over on how he chooses a representation of data modeling. He bases it on two factors: something that is able to be quickly sketched on the front board in class, and something that students will be able to understand and emulate through SQL statements. Watson then goes on to his teaching method of “integrated spiral approach,” which means that he teaches data modeling and SQL side by side so that the students can make the connection and begin to see the connections between the two as opposed to the general teaching of data modeling followed by SQL. In the end, Watson says that its not how you represent the final data model, but that the data model grasps the true nature of the project. read more...

Understand the Data in Data Modeling {4}

by Penny P
In the article that I read, it said that when you start working on data modeling you’re eventually working on something that will lead to database design. Before data modeling become popular, some people saw data administration and information groups as obstacles because it slowed down development. However, companies soon came to the conclusion that database models can actually serve as framework for new applications to be designed. New applications get created for different tasks while the old ones get integrated with the new. read more...

ER Modeling for iPad {1}

by Alexander V

 

Summary:

The article relates to the week’s lecture in that it relates to ER modeling. The article was about an update to a piece of data modeling software for the iPad. The company, Permeative Technologies, is known for making “drawing apps’ and distributing their apps through the app store. They recently updated their ER modeling software, Draw ER, for the iPad to version 1.2. The app allows users to easily create ER diagrams quickly right from their iPad. Draw ER has most of the functions of modeling software such creating entities and relationships. A diagram can be created by dragging shapes from a menu onto a work area. The software has a couple of notable features such as: working on multiple sheets simultaneously, re-sizable work area, and easy to draw simple diagrams. The software can be purchased for only $0.99. read more...

Wanted: Database Models {Comments Off on Wanted: Database Models}

by James C
Summary:

The topic of data modeling has always been hard for students to grasp. Even though the there are many techniques on data modeling, no one standardized method has been agreed on by educational institutions. In order for developers to understand the connections between entities and their relationships they first must study the entity relationship (ER) modeling technique. Despite the effectiveness of this technique, though, many developers, as seen through their work, are still having trouble using, learning, and integrating with it. To add to this dilemma, many developers are also having additional issues with combining the object-oriented approach with the entity relationship modeling technique. This article sheds some light on the subject of which modeling technique is more effective, the UML or ER modeling technique. The debate between the better of the two are is not answered, but rather explored. Both methods having similar issues, like dealing with multi-valued attributes, for example. One real issue that did arise in the end was that database designers and system analysts are in constant disagreement. Both systems analysts and database designers are both comfortable with different ideas. SA’s are at ease with object-oriented programming methods. Database designers are more structured and mathematically centered. read more...

Time to move on to something…better {1}

by Stephen O
Summary:

When is it time for something new? When is a good time to trade up? Is it similar to buying a smart phone? Waiting for the new model later that year? Is it when the industry chooses a standard like Blue Ray or VHS? On the other hand, is it like buying a car and it no longer can perform reliably the duties we purchased it for? When is it time for us to transition to the next generation of Data Modeling?  In the article “Toward a Next Generation Data Modeling Facility: Neither the Entity-Relationship Model nor UML Meet the Need” the author went about explaining why perhaps it is time to move on towards the next generation of Data Modeling.  They defined five wanted characteristics of a Data model. read more...