cs 405g: introduction to database systems 26 final exam review chen qian university of kentucky
TRANSCRIPT
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CS 405G: Introduction to Database Systems
26 Final exam reviewChen Qian
University of Kentucky
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Final exam
Tuesday 05/05/14 10:30 – 12:00 This classroom.
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Read the mid-term review
ER diagram Relational Algebra SQL (important!)
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Functional dependencies
A functional dependency (FD) has the form X -> Y, where X and Y are sets of attributes in a relation R
X -> Y means that whenever two tuples in R agree on all the attributes in X, they must also agree on all attributes in Y
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FD examples
Address (street_address, city, state, zip) street_address, city, state -> zip zip -> city, state zip, state -> zip?
This is a trivial FD Trivial FD: LHS RHS
zip -> state, zip? This is non-trivial, but not completely non-trivial Completely non-trivial FD: LHS ∩ RHS = ?
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Attribute closure
Given R, a set of FD’s F that hold in R, and a set of attributes Z in R:The closure of Z (denoted Z+) with respect to F is the set of all attributes {A1, A2, …} functionally determined by Z (that is, Z -> A1 A2 …)
Algorithm for computing the closure Start with closure = Z If X -> Y is in F and X is already in the closure, then also
add Y to the closure Repeat until no more attributes can be added
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Using attribute closure
Given a relation R and set of FD’s F Does another FD X -> Y follow from F?
Compute X+ with respect to F If Y X+, then X -> Y follow from F
Is K a super key of R? Compute K+ with respect to F If K+ contains all the attributes of R, K is a super key
Is a super key K a key of R? Test where K’ = K – { a | a K} is a superkey of R for all
possible a
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Rules of FD’s
Armstrong’s axioms Reflexivity: If Y X, then X -> Y Augmentation: If X -> Y, then (X,Z) -> (Y,Z) for any Z Transitivity: If X -> Y and Y -> Z, then X -> Z
Rules derived from axioms Splitting: If X -> YZ, then X -> Y and X -> Z Combining: If X -> Y and X -> Z, then X -> YZ
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First Normal Form ( 1NF )
A relation is in first normal form if the domain of each attribute contains only atomic values, and the value of each attribute contains only a single value from that domain.
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2nd Normal Form
An attribute A of a relation R is a nonprimary attribute if it is not part of any key in R, otherwise, A is a primary attribute.
R is in (general) 2nd normal form if every nonprimary attribute A in R is not partially functionally dependent on any key of R
How to identify 2NF How to decompose relations
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Third normal form
• 3NF requires that there are no non-trivial functional dependencies of non-key attributes on something other than a superset of a candidate key.
• Recall: non-trivial FD means LHS has no intersection with RHS.
• In summary, all non-key attributes are mutually independent.
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• A table is said to be in the BCNF if and only if it is in the 3NF and every non-trivial, left-irreducible functional dependency has a candidate key as its determinant.
•How to find violations
•How to decompose relations
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BC normal form
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Conflicts
precedence graph conflict-serializable schedule
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Lock
exclusive lock and shared locks
Two-phase locking All lock requests precede all unlock requests
Strict 2PL Only release locks at commit/abort time
Examples
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Disk
Disk structure Cylinder, platter, track, etc.
Random disk access Seek time + rotational delay + transfer time
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File Storage
Heap file as a list or page directory Record format Page layout
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Tree-Structured Indexes: Introduction
Tree-structured indexing techniques support both range selections and equality selections.
ISAM =Indexed Sequential Access Method static structure; early index technology.
B+ tree: dynamic, adjusts gracefully under inserts and deletes.
Operations: search, range query, insert, delete (important!)
Understand the examples in the exercise slides!
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Hashing
Static hashing
Dynamic hashing Extensible and linear hashing
Understand examples in slides
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Final Exam
1. True/False 2. Functional Dependency and Normal Forms 3. SQL 4. Index (B+ Tree) 5. Index (B+ Tree) 6. Storage
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Good luck and hope you enjoy this class!
Don’t forget: You give me a grade
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