Chapter 6 - Data Modeling Flashcards
What is a data model?
A data model is a formal way of representing the data that are used and created by a business system, and how those data are related to one another.
What is an entity-relationship diagram?
An entity-relationship diagram is a graphical illustration that shows the information that is created, stored, and used by a business system.
What are entities?
Entities are similar kinds of information, also referred to as classes in some cases. It is the most basic building block of a data model. It can be a person, place, event, or thing, as long as data is being collected on it.
Entities represent things that have multiple instances/occurrences.
What is an attribute?
An attribute is some type of information that is captured about an entity. Attributes are always nouns that are listed with an entity. Some attributes are unique, and can be serve as the entity’s identifier, or primary key.
What are identifiers? Concatenated identifiers? Give an example of each.
An identifier is an attribute of an entity that can be used to identify individual instances of that entity. A concatenated identifier is a set of attributes that, together, are unique and can serve as an identifier.
What are relationships?
A relationship is an association between entities. Each relationship has a parent and a child entity, and should be labeled with a verb.
What is cardinality? What are the three types of cardinality relationships?
Cardinality is the ratio at which parent instances of an entry exist in proportion to child instances. The three types of cardinality relationships are:
- 1:1 Relationship
- 1:M Relationship
- M:N Relationship
What is modality?
Modality is a way of describing whether or not a relationship is “optional”, or whether or not a child entity can exist without a related instance of the parent entity.
What is a data dictionary?
A data dictionary is a document or database that contains the metadata on a data, that is, data about the data. Information on the entities, attributes, and relationships on the ERD.
What are the steps involved in creating an ERD?
The steps to create an ERD are as follows:
- Identify the entities
- Add attributes to each entity
- Draw relationships between each entity
What is an independent entity?
An independent entity is an entity that can exist without other entities to support it. Things like cars, pencils, customers, all exist without the need for other entities.
What is a dependent entity?
A dependent entity is an entity that requires attributes from other entities to be identifiable. Things like “movie ticket” cannot exist without there being a “movie”.
What is an intersection entity?
An intersection entity is an entity that is created to divide a M:N relationship, allowing for information on their relationship to be shared.
What is normalization?
Normalization is a technique by which a series of rules are applied to a logical data model (ERD in this case) to determine how well formed it is.
What is needed for an ERD to be in 1NF?
For an ERD to be in 1NF, no attributes in any entities can contain more than one value for a single instance. For example, Phone can only contain one phone number, not a work phone AND a cell phone.
In addition, there cannot be any attributes with repeating values. Things like “AUTHOR1”, “AUTHOR2”, and so on.
What is needed for an ERD to be in 2NF?
For an ERD to be in 2NF, all non-key attributes must be fully dependent on the entire primary key. This means that, if there is a composite primary key, all non-key attributes must be dependent on all parts of the composite key, and not just one.
What is needed for an ERD to be in 3NF?
For an ERD to be in 3NF, it cannot have any transitive functional dependencies. This means that, in a table with attributes A, B, and C, if B is dependent on A, and C is dependent on B, C is TRANSITIVELY dependent on A. This is bad.
What does it mean for an ERD to be balanced with the DFDs?
For the DFDs to be balanced with an ERD, the data components (that is, data and stat stores) need to be in balance. This means that the data stores on the DFD need to correspond with the entities and attributes in the ERD.
