Slides are here . Here’s a handy Crow’s Foot quick reference from Vivek M. Chawla. It doesn’t include attributes in the entities, but several authors and some company guidelines do include them when
necessary to make a point. We begin the database design process with the conceptual model. Various styles of notation are used across the industry. We will use the crows-foot style. In the conceptual model we will build and ERD diagram which only addresses entities and relationships and cardinality. The second model is the logical model. In this model we populate the entity representation from the previous model with attributes and their generic types. We also identify the
keys to be used. The third model is the physical model. This is the only one of the three models that actually considers the specific database technology to be used. The first two models could be used with any database technology and, so, are written generically. The physical model specifies the precise data types of the attributes of the entities (relations). There are tools available to aid these design steps. In particular, MySQLWorkbench can turn a
completed ERD directly into the MySQL commands to create the entities and relations. It’s less helpful in the earlier stages. Entity Relationship Model (ERM)The basis of an entity relationship diagram (ERD) which depicts the:
He also did the same analysis for Chinese characters. Attributes
RelationshipsAn association between entities, typically meaningful in both directions
Entities can either exist on their own or they can only exist when associated with some other entity type.
SLIDE 8
Developing an ER Diagram
Conflicting GoalsOnly the simplest databases can achieve all of these guidelines and goals. You will often be faced with conflicting goals. Slide 28
The special case of the 1:1 recursive relationshipThis kind of relationship occurs often and the first time you see it, it’s rather puzzling as to how to design and implement it. Slide 29
 What is a term used to describe the relationship between two entities?An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can exist between entities (instances of those entity types).
Which relationship is one in which a relationship exists between occurrences of the same entity set?Unary relationship (recursive)
A unary relationship, also called recursive, is one in which a relationship exists between occurrences of the same entity set. In this relationship, the primary and foreign keys are the same, but they represent two entities with different roles.
What is a type of attribute?An attribute type definition specifies the attribute's syntax and how attributes of that type are compared and sorted. The attribute types in the directory form a class hierarchy. For example, the "commonName" attribute type is a subclass of the "name" attribute type.
What is an entity that is existence independent that is it can exist apart from all of its related entities?Strong Entities: If an entity can exist apart from all its related entities, then it is existence-independent and it is referred to as strong entity or regular entity. The concept of relationship strength is related on how primary keys (PK) are defined among entities.
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