stk-databaseDesign2
What are the different types of relationships?
1 : 1 1 : M M : 1 M : M
When all attributes are single-valued, the database model is said to conform to:
1st Normal Form
When you resolve a M-M by creating an intersection entity, this new entity will always inherit:
A relationship to each entity from the original M-M.
When you add the concept of time to your data model, you are:
Adding complexity to your model.
What is the rule of Second Normal Form?
All non-UID attributes must be dependent upon the entire UID
What is the function of logging or journaling in conceptual data models?
Allows you to track the history of attribute values, relationships and/or entire entities
Many to many relationships between entities usually hide what?
An Entity
To visually represent exclusivity between two or more relationships in an ERD you would most likely use ?
An arc
A UID can be made up from...
Attributes and/or Relationships
If an intersection entity is formed that contains no attributes of its own, its uniqueness may be modeled by
Barring the relationships to the original entities
You are doing a data model for a computer sales company, where the price goes down on a regular basis. If you want to allow them to modify the price and keep track of the changes, what is the best way to model this?
Create a product entity and a related price entity with start and end dates, and then let the users enter the new price whenever required. Use a price entity with a start and end date
A non-transferable relationship is represented by which of the following symbols?
Diamond
A relationship can be both recursive and hierachal at the same time. True or False?
False
A unique identifier can only be made up of one attribute. True or False?
False
If the entity CD has the attributes: #number, *title, *producer, *year, o store name, o store address, this entity is in 3rd Normal Form ("no non-UID attribute can be dependent on another non-UID attribute). True or False?
False
No databases in the world is ever truly on 3rd Normal Form. Everyone always stops after 2nd Normal Form. True or False?
False
There are no formal rules for how to draw ERD's. The most important thing is to make sure all entities, attributes and relationships are documented on diagram. The Layout is not significant. True or False?
False
You must make sure all entities of a proposed system can fit onto one diagram. It is not allowed to break up a data model into more than one diagram. True or False?
False
Historical data should ALWAYS be kept. True or False?
Fasle
What is the benefit to the users of a system that includes "time," e.g. Start Date and End Date for Employees?
Increased usability and flexibility of a system;
What uncommon relationship is described by the statements: "Each LINE must consist of many POINTS and each POINT must be a part of many LINES"
M : M
When data is stored in more than one place in a database, the database violates the rules of ___________.
Normalisation
Modeling historical data produces efficient ways for a business to ..
Providing valuable information via reports to management
If the same relationship is represented twice in an Entity Relationship Model, it is said to be:
Redundant
What part of an erd can you add an arc to?
Relationship
Why would you want to model a time component when designing a system that lets people buy bars of gold?
The price of gold fluctuates and for determining price, you need to know the time of purchase
Two ways to enhance the readability of an ERD is :
There should be no crossing lines. All crows feet (Many-ends) of relationships should point the same way.
If a relationship can be moved between instances of the entities it connects, it is said to be:
Transferable
A recursive rationship should not be part of a UID. True or False?
True
All parts of a UID are mandatory. True or False?
True
An entity can only have one UID. True or False?
True
As a database designer it is your job to store data in only one place and the best place. True or False?
True
Generic models are generally less complex than a specific model. True or False?
True
It is a good idea to group your entities in a diagram according to the expected volumes. By grouping high volume entities together, the diagrams could become easier to read. True or False?
True
It is desirable to have an entity called DAY with a holiday attribute when you want to track special holidays in a payroll system. True or False?
True
Modeling historical data can produce a unique identifier that includes a date. True or False?
True
Non-transferable relationships can only be mandatory, not optional. True or False?
True
When are relationships unnecessary?
When you can derive the relationship from other relationships in the model
People are not born with "numbers," but a lot of systems assign student numbers, customer IDs, etc. A shoe has a color, a size, a style, but may not have a descriptive "number". So, to be able to uniquely and efficiently identify one instance of the entity SHOE, a/an ______________ UID can be created.
Artificial
All data models MUST have some portions of the model modeled as a generic component. True or False?
False
An entity can have repeated values and still be in 1st Normal Form. True or False?
False
Audit trail attributes cannot be placed in the entities they are auditing, they must be placed in separate, new entities, created just for that purpose. True or False?
False
How do you know when to use the different types of time in your design?
It depends on the functional needs of the system
When resolving an M:M relationship, the new relationships will always be __________ on the many side.
Mandatory
What is the definition for Third Normal Form?
No non-UID attribute can be dependent on another non-UID attribute
If you are tracking employment dates for an employee, do you need to have an "End Date" attribute?
Yes, if the company wants to track employee information, like multiple start and end dates
When you transform a specific model to be generic :
You tend to end up with fewer entities in the generic model than you had in the specific model Either all or none of the original attributes make it into the generic model.
