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DatabaseEmergency

database systems

QuestionAnswer
3 kinds of schema, what are they? External, internal, conceptual
describe external schema view closest to users. User view; shows what a particular user group is interested in and hides the rest of the DB from them
describe conceptual level describes the database for a community of users; hides details of physical storage, contains constraints, data types, relationships, user operations and entities; created by the DBA
what's data independence Logical independence, you can change up the conceptual schema without having to change the external schema or application programs
what's physical independence you can change the physical (internal level) without changing the conceptual schema
candidate key If you have 2 keys, choose one as the primary and the other is the candidate key which could potentially switch roles with the original primary key
primary key unique & non, redundant, that distinguishes tuple from table (can have single or multi variable attributes)
foreign key not a key but an attribute so a connection can be made
Entity Integrity constraint no primary key value can be NULL
referential integrity constraint maintains consistency between 2 tuples
3 operations on a DB Insert Delete Update
Insert's constraint violations Domain integrity Key integrity violation Entity integrity violation Referential integrity violation
Domain integrity violation wrong data type or not in this defined domain
key integrity violation duplicate key in this table (two same SSN's)
Entity integrity violation Primary key has a null value
referential integrity violation foreign key of new entity doesn't have a primary key to reference
Delete violates only this integrity referential integrity (you got rid of a tuple that had a primary key someone was looking at)
what is done when delete violates referential integrity? 1 Reject the deletion 2 cascade 3 set the refernced tuple to NULL or default
Update's violations are... the exact same as INSERT's
define a view virtual/derived/not-real table that can only be built on the base table
Technical factor to consider in choosing a DB 1 DDl's and DML's must be compared 2 Storage of the system must be compared 3 Access path to know how the data will be retrieved 4 user interface 5 Backup & recovery procedure 6 Security/Integrity 7 Built-in-functions to make programming easier
define normalization process of analyzing relation schema to get 1 minimized redundancy 2 minimize the insertion, deletion and update anomalies
1st normal form the only attribute values are atomic (pretty much means each cell only has a single value & no duplicate rows)
2nd normal form everything that's in the relational table is completely dependent on the primary key of that table
3rd normal form 2nd normal form but no attributes are transitively dependent on a relational primary key from the same table (see p524 in textbook if this is confusing)
3 ways to store on a disk sequential organization direct organization Indexed sequential
Sequential Organization stored one after the other with sequential access
direct organization the disk address & data ID have direct access
indexed sequential looks at groups of addresses one after another
3 things to know about physical design 1 file organization (see ways to store on disk) 2 choices to improve response time 3 factors that influence physical DB design
Things to improve retrieval 1 Response time 2 throughput 3 space utilization
Factors that influence database designs 1 Queries/transactions-what kind of queries 2 Analyzing the expected freq of the queries-how often is a query used 3 Analyzing the time constraint 4 Analyzing the expected frequency of updated operations 5 Analyzing the uniqueness of analyzed attribut
Describe internal schema Describes the physical storage structure of the DB which includes data storage and access paths
Created by: truPrince