Download 3902 Chapter 1

Summary: Database Systems
• Introduction to the database systems (1)
- What is a database
- The main characters of a database
- The basic database design method
- The entity-relationship data model for application
modeling
• Concepts and Architecture
- Database schema, Schema evolution, Database state
- Working process with a database system
- Database system architecture
- Data independence concept
Sept. 2004
Yangjun Chen
91.3902
1
Summary: Database Systems
• Data modeling using ER-model (2)
- Entity-relationship model
- Entity types
- strong entities
- weak entities
- Attributes - attribute classification
- Relationships among entities
- Constraints
- cardinality constraints
- participation constraints
- ER-to-Relation-mapping
Sept. 2004
Yangjun Chen
91.3902
2
Summary: Database Systems
• Hashing technique (3)
- external hashing
- static hashing & dynamic hashing
- hash function
- mathematical function that maps a key to a bucket
address
- collisions
collision resolution scheme
- open addressing
- chaining
- multiple hashing
- linear hashing
Sept. 2004
Yangjun Chen
91.3902
3
Summary: Database Systems
• Multi-level index (4)
- tree
- root, internal, leaf, subtree
- parent, child, sibling
- balanced, unbalanced
- b+-tree
- splits on overflow; merge on underflow
- in practice it is usually 3 or 4 levels deep
- search, insert, delete algorithms
Sept. 2004
Yangjun Chen
91.3902
4
Summary: Database Systems
• Data modeling using Relational model Relational algebra (5)
- Relational Data Model
- relational schema, relations
- database schema, database state
- integrity constraints and updating
- Relational algebra
- select, project, join, cartesian product
- set operations:
union, intersection, difference
- division
Sept. 2004
Yangjun Chen
91.3902
5
Summary: Database Systems
• SQL (6)
- DDL
- creating schemas
- modifying schemas
- DML
- select-from-where clause
- group by, having, order by
- update
- view
Sept. 2004
Yangjun Chen
91.3902
6
Summary: Database Systems
• ER-to-Relation mapping (7)
General process
1. Create a relation for each strong entity type
2. Create a relation for each weak entity type
3. For each binary 1:1 relationship choose an entity and include the
other’s PK in it as an FK
4. For each binary 1:n relationship, choose the n-side entity and include
an FK wrt the other entity.
5. For each binary M:N relationship, create a relation for the
relationship
6. For each multi-valued attribute create a new relation
7. For each n-ary relationship, create a relation for the relationship
Sept. 2004
Yangjun Chen
91.3902
7
Summary: Database Systems
• ER-to-Relation mapping (7)
4 choices (for handling is-a relationship):
1. Create separate relations for the supertype and each of
the subtypes.
2. Create relations for the subtypes only - each contains
attributes from the supertype.
3. (disjoint subtypes) Create only one relation - includes
all of the attributes for the supertype and all for the
subtypes, and one discriminator attribute.
4. (overlapping subtypes) Create only one relation includes all of the attributes for the supertype and all for
the subtypes, and one logical discriminator attribute per
subtype.
Sept. 2004
Yangjun Chen
91.3902
8
Summary: Database Systems
• Normalization (8)
- Function dependency
We say a functional dependency exists between the
attributes X and Y: X  Y, if, whenever a tuple exists
with the value x for X, it will always have the same
value y for Y.
- Inference rules for function dependencies
- 1NF - First Normal Form
The domain of an attribute must only contain atomic
values.
Sept. 2004
Yangjun Chen
91.3902
9
Summary: Database Systems
• Normalization (8)
- 2NF - Second Normal Form
A relation schema is in 2NF if
(1) it is in 1NF and
(2) every non-key attribute must be fully functionally
dependent on the primary key.
- 3NF - Second Normal Form
A relation schema is in 3NF if
(1) it is in 2NF and
(2) each non-key attribute must not be fully functionally
dependent on another non-key attribute (there must be no
transitive dependency of a non-key attribute on the PK)
Sept. 2004
Yangjun Chen
91.3902
10
Summary: Database Systems
• Normalization (8)
- Boyce Codd Normal Form, BCNF
Consider a different definition of 3NF, which is equivalent
to the previous one.
A relation schema R is in 3NF if, whenever a function
dependency X  A holds in R, either
(a) X is a superkey of R, or
(b) A is a prime attribute of R.
Removing (b), we have the definition for BCNF.
Sept. 2004
Yangjun Chen
91.3902
11
Summary: Database Systems
• Lossless Join (9)
- Decomposition of a relation schema
Emp_PROJ
SSN
PNUM
hours
ENAME
PNAME
PLOCATION
F = {SSN  ENAME, PNUM  {PNAME, PLOCATION},
{SSN, PNUM}  hours}
R1
R2
SSN
ENAME
SSN
PNUM
PNUM
PNAME
PLOCATION
R3
Sept. 2004
hours
Yangjun Chen
91.3902
Lossless join
12
Summary: Database Systems
• Lossless Join (9)
- Matrix for a decomposition
A1
SSN
A2
ENAME
A3
PNUM
A4
PNAME
A5
PLOCATION
A6
hours
R1
b11
b12
b13
b14
b15
b16
R2
b21
b22
b23
b24
b25
b26
R3
b31
b32
b33
b34
b35
b36
- Matrix transformation to check the lossless join property
Sept. 2004
Yangjun Chen
91.3902
13
Summary: Database Systems
• Lossless Join (9)
R1
a1
a2
b13
b14
b15
b16
R2
b21
b22
a3
a4
a5
b26
R3
a1
b32
a3
b34
b35
a6
SSN  ENAME
SSN
ENAME
R1
a1
a2
b13
b14
b15
b16
R2
b21
b22
a3
a4
a5
b26
R3
a1
a2
a3
b34
b35
a6
Sept. 2004
Yangjun Chen
91.3902
14
Summary: Database Systems
• Lossless Join (9)
PNUM  {PNAME, PLOCATION}
PNUM
PNAME
PLOCATION
R1
a1
a2
b13
b14
b15
b16
R2
b21
b22
a3
a4
a5
b26
R3
a1
a2
a3
a4
a5
a6
Sept. 2004
Yangjun Chen
91.3902
15
Summary: Database Systems
• Deductive Databases (10)
- A deductive database can be defined as an advanced
database augmented with an inference system.
- well-formed formulas
- clause and Horn-clause
- Bottom-up and top-down evaluation of non-recursive
queries.
- Naive and semi-naive evaluation of recursive queries.
Sept. 2004
Yangjun Chen
91.3902
16
Summary: Database Systems
• Hierarchical Databases (11)
- Hierarchical schema
- PCR relationship
- PCR occurrence and hierarchical occurrence
- Virtual PCR
- Data definition and data manipulation in hierarchical
schema
Sept. 2004
Yangjun Chen
91.3902
17