Section 6 Flashcards
A UID that is a single attribute is a ……….. ……….
simple UID
However, sometimes a single attribute is not enough to uniquely identify an instance of an entity. If the UID is a combination of attributes, it is called a ………… ……….
composite UID
The date of performance or seat number alone does not identify a concert ticket. On any given date, there are many seats available. The same seat number is sold for many different dates.
………… …………. are those that don’t occur in the natural world but are created for purposes of identification in a system
Artificial UIDs
A UID can be both artificial and ………….
composite
R 1
It is possible for an intersection entity to use an artificial attribute as the UID, instead of the barred relationships to the originating entities
R 2
Sometimes two or more possible UIDs exist. For example, when you order a product from a commercial website, you will usually be assigned a unique customer code and asked to enter your e-mail address. Each of these uniquely identifies you, and each could be chosen as the UID. These are both ………… ……….
candidate UIDs
Sometimes two or more possible UIDs exist. For example, when you order a product from a commercial website, you will usually be assigned a unique customer code and asked to enter your e-mail address. Each of these uniquely identifies you, and each could be chosen as the UID. These are both ………… ……….
candidate UIDs
Only one of the candidate UIDs is chosen as the actual UID, this is called the ……… ………. The other candidates are called ……….. ………..
primary UID
secondary UIDs
Secondary UIDs can be useful as an alternative means of …………………………..
searching for data.
- You forgot your student ID, but you have your badge with you.
- You have a frequent-shopper card at the supermarket but did not bring it with you. Some systems can find your information if you provide your telephone number.
R 2
…………………..: A series of steps followed to obtain a database design that allows for efficient access and storage of data in a relational database. These steps reduce data redundancy and the chances of data becoming inconsistent (because two copies and somebody update only one of them).
Normalization
useful memory aid: some legal systems require that a witness in court swears to tell “the truth, the whole truth and nothing but the truth”. One way of stating the normalization rules is that “Every non-UID attribute must be dependent on the UID, the whole UID, and nothing but the UID”.
One of your goals as a database designer is to “store information in …… ………. and in the best possible place“
one place
1NF eliminates repeating groups (multiple values) within an attribute by transferring the attribute to a
new entity and then connecting the entities with a ………. relationship.
1:M
Following the rules of 2NF allows us to validate that every attribute is in the correct …………, and identify entities that may have been missed in our original ERD.
entity
Note that the rule of Second Normal Form states that any …………. field must be dependent on the ……………
non-UID / entire UID
An entity is considered to be in 2NF if the UID of the entity is ………….
simple
The rule of Third Normal Form (3NF) states that no ……….. attribute can be dependent on another ………… attribute
non-UID
A ………. ………… exists when any attribute in an entity is dependent on any other non-UID attribute in that entity
transitive dependency
Third normal form: The form of database normalization where all non key fields are dependent on the key, the whole key, and nothing but the key
Third Normal Form ………… transitive dependencies
prohibits
Third Normal Form Violations are hiding ………. ………
another entity.
For an entity to be in Third Normal Form, it must also be in ……… ……… ………..
Second Normal Form
