Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
16 Cards in this Set
- Front
- Back
|
When/ Why do you need a database |
When you need to make ad hock queries. When you have concurrent transactions. NOT when you have a lot of data |
|
|
Data Independence |
The underlying data implementation does not change how the user interacts with the database |
|
|
When to use NoSQL |
-Non-relational DB -dealing with things like text -Unstructured data -Facebook/twiutter data -Queries are limited to a small subset of queries -Dont ask queries with a lot of logic |
|
|
When to use SQL |
-When you have structured data -AD HOCK QUERIES -Transactions with read and write conflicts |
|
|
Do relationships have to be binary? |
NO |
|
|
Can Every relationship be a binary relationship? |
No |
|
|
Does a subclass have more or less properties than the main class? |
Subclass has MORE properties (attributes in ER diagram) ex: the table Beers has: Name, Manufacturer |
|
|
What is a Key |
A set of attributes that identifies an entity uniquely |
|
|
Lossless Join |
Deconstructing a table into multiple smaller tables without losing any information |
|
|
Armstrong Axioms |
Reflexivity X->Y if Y if Y is a subset of X Augmentation X->Y then ZX ->Y Transitivity A->B B->C, then A->C |
|
|
As you add more tuples you get less dependencies |
Because there becomes more chance of a counter example. If you fill the table up to infinity, you will eventually get no FD's |
|
|
True/False: If i keep adding tuples to a table, eventually i will get to a vpoint where only trivial instances define dependencies |
True |
|
|
Can I Always decompose into BCNF form? |
YES. Binary tables are always in BCNF (either no dependencies or you have A->B or B->A). Tables with no FD's are already in BCNF |
|
|
What are the ACID Properties |
Atomicity - either transactions happen completely, or not at all Consistancy =- execution of a transaction happens in isolation and does not effect the consistancy of the DB Isolation - although multiple transactions can happen simukltaniously, the results will be the same as if they were executed serially Durability - once a transaction has been committed, it will remain so |
|
|
Why do we care about serializability? |
It guarantees the consistancy of the database |
|
|
Two phase locking Format: |
Lock(A), Lock(B), Unlock(B), Unlock(A) |
