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Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Lecture 13 of 42
Wednesday, 19 September 2007
William H. HsuDepartment of Computing and Information Sciences, KSU
KSOL course page: http://snipurl.com/va60Course web site: http://www.kddresearch.org/Courses/Fall-2007/CIS560
Instructor home page: http://www.cis.ksu.edu/~bhsu
Reading for Next Class:Section 6.1 – 6.2, Silberschatz et al., 5th edition
Database Design OverviewNotes: Relational Calculi, PS3
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Modification of the Database – Deletion
Deletion of tuples from a relation is expressed by use of a D. command. In the case where we delete information in only some of the columns, null values, specified by –, are inserted.
Delete customer Smith
Delete the branch_city value of the branch whose name is “Perryridge”.
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Deletion Query Examples Delete all loans with a loan amount greater than $1300 and less
than $1500. For consistency, we have to delete information from loan and
borrower tables
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Deletion Query Examples (Cont.)
Delete all accounts at branches located in Brooklyn.
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Modification of the Database – Insertion
Insertion is done by placing the I. operator in the query expression.
Insert the fact that account A-9732 at the Perryridge branch has a balance of $700.
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Modification of the Database – Insertion (Cont.)
Provide as a gift for all loan customers of the Perryridge branch, a new $200 savings account for every loan account they have, with the loan number serving as the account number for the new savings account.
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Modification of the Database – Updates
Use the U. operator to change a value in a tuple without changing all values in the tuple. QBE does not allow users to update the primary key fields.
Update the asset value of the Perryridge branch to $10,000,000.
Increase all balances by 5 percent.
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Microsoft Access QBE Microsoft Access supports a variant of QBE called Graphical
Query By Example (GQBE) GQBE differs from QBE in the following ways
Attributes of relations are listed vertically, one below the other, instead of horizontally
Instead of using variables, lines (links) between attributes are used to specify that their values should be the same.Links are added automatically on the basis of attribute name, and the
user can then add or delete linksBy default, a link specifies an inner join, but can be modified to specify
outer joins. Conditions, values to be printed, as well as group by attributes are all
specified together in a box called the design grid
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
An Example Query in Microsoft Access QBEAn Example Query in Microsoft Access QBE
Example query: Find the customer_name, account_number and balance for all accounts at the Perryridge branch
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
An Aggregation Query in Access QBEAn Aggregation Query in Access QBE
Find the name, street and city of all customers who have more than one account at the bank
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Aggregation in Access QBE The row labeled Total specifies
which attributes are group by attributes which attributes are to be aggregated upon (and the aggregate
function). For attributes that are neither group by nor aggregated, we can
still specify conditions by selecting where in the Total row and listing the conditions below
As in SQL, if group by is used, only group by attributes and aggregate results can be output
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Banking Example branch (branch_name, branch_city, assets ) customer (customer_name, customer_street, customer_city ) account (account_number, branch_name, balance ) loan (loan_number, branch_name, amount ) depositor (customer_name, account_number ) borrower (customer_name, loan_number )
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Chapter 6: Entity-Relationship Model
Design Process Modeling Constraints E-R Diagram Design Issues Weak Entity Sets Extended E-R Features Design of the Bank Database Reduction to Relation Schemas Database Design UML
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Modeling
A database can be modeled as: a collection of entities, relationship among entities.
An entity is an object that exists and is distinguishable from other objects. Example: specific person, company, event, plant
Entities have attributes Example: people have names and addresses
An entity set is a set of entities of the same type that share the same properties. Example: set of all persons, companies, trees, holidays
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Entity Sets customer and loancustomer_id customer_ customer_ customer_ loan_ amount name street city number
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Relationship Sets
A relationship is an association among several entitiesExample:
Hayes depositor A-102customer entity relationship set account entity
A relationship set is a mathematical relation among n 2 entities, each taken from entity sets
{(e1, e2, … en) | e1 E1, e2 E2, …, en En}
where (e1, e2, …, en) is a relationship Example:
(Hayes, A-102) depositor
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Relationship Set borrower
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Relational Database Design
Features of Good Relational Design Atomic Domains and First Normal Form Decomposition Using Functional Dependencies Functional Dependency Theory Algorithms for Functional Dependencies Decomposition Using Multivalued Dependencies More Normal Form Database-Design Process Modeling Temporal Data
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
The Banking Schema branch = (branch_name, branch_city, assets) customer = (customer_id, customer_name, customer_street, customer_city) loan = (loan_number, amount) account = (account_number, balance) employee = (employee_id. employee_name, telephone_number, start_date) dependent_name = (employee_id, dname) account_branch = (account_number, branch_name) loan_branch = (loan_number, branch_name) borrower = (customer_id, loan_number) depositor = (customer_id, account_number) cust_banker = (customer_id, employee_id, type) works_for = (worker_employee_id, manager_employee_id) payment = (loan_number, payment_number, payment_date,
payment_amount) savings_account = (account_number, interest_rate) checking_account = (account_number, overdraft_amount)
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Combine Schemas?
Suppose we combine borrow and loan to get bor_loan = (customer_id, loan_number, amount )
Result is possible repetition of information (L-100 in example below)
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
A Combined Schema Without Repetition
Consider combining loan_branch and loanloan_amt_br = (loan_number, amount, branch_name)
No repetition (as suggested by example below)
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
What About Smaller Schemas?
Suppose we had started with bor_loan. How would we know to split up (decompose) it into borrower and loan?
Write a rule “if there were a schema (loan_number, amount), then loan_number would be a candidate key”
Denote as a functional dependency: loan_number amount
In bor_loan, because loan_number is not a candidate key, the amount of a loan may have to be repeated. This indicates the need to decompose bor_loan.
Not all decompositions are good. Suppose we decompose employee intoemployee1 = (employee_id, employee_name)employee2 = (employee_name, telephone_number, start_date)
The next slide shows how we lose information -- we cannot reconstruct the original employee relation -- and so, this is a lossy decomposition.
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
A Lossy Decomposition
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
First Normal Form
Domain is atomic if its elements are considered to be indivisible units Examples of non-atomic domains:
Set of names, composite attributes Identification numbers like CS101 that can be broken up into parts
A relational schema R is in first normal form if the domains of all attributes of R are atomic
Non-atomic values complicate storage and encourage redundant (repeated) storage of data Example: Set of accounts stored with each customer, and set of
owners stored with each account We assume all relations are in first normal form (and revisit this in
Chapter 9)
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Microsoft Access QBE Microsoft Access supports a variant of QBE called Graphical
Query By Example (GQBE) GQBE differs from QBE in the following ways
Attributes of relations are listed vertically, one below the other, instead of horizontally
Instead of using variables, lines (links) between attributes are used to specify that their values should be the same.Links are added automatically on the basis of attribute name, and the
user can then add or delete linksBy default, a link specifies an inner join, but can be modified to specify
outer joins. Conditions, values to be printed, as well as group by attributes are all
specified together in a box called the design grid
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Modeling
A database can be modeled as: a collection of entities, relationship among entities.
An entity is an object that exists and is distinguishable from other objects. Example: specific person, company, event, plant
Entities have attributes Example: people have names and addresses
An entity set is a set of entities of the same type that share the same properties. Example: set of all persons, companies, trees, holidays
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Entity Sets customer and loancustomer_id customer_ customer_ customer_ loan_ amount name street city number
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Relationship Sets
A relationship is an association among several entitiesExample:
Hayes depositor A-102customer entity relationship set account entity
A relationship set is a mathematical relation among n 2 entities, each taken from entity sets
{(e1, e2, … en) | e1 E1, e2 E2, …, en En}
where (e1, e2, …, en) is a relationship Example:
(Hayes, A-102) depositor
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Relationship Set borrower
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Relationship Sets (Cont.)
An attribute can also be property of a relationship set. For instance, the depositor relationship set between entity sets
customer and account may have the attribute access-date
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Degree of a Relationship Set
Refers to number of entity sets that participate in a relationship set.
Relationship sets that involve two entity sets are binary (or degree two). Generally, most relationship sets in a database system are binary.
Relationship sets may involve more than two entity sets.
Relationships between more than two entity sets are rare. Most relationships are binary. (More on this later.)
Example: Suppose employees of a bank may have jobs (responsibilities) at multiple branches, with different jobs at different branches. Then there is a ternary relationship set between entity sets employee, job, and branch
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Attributes
An entity is represented by a set of attributes, that is descriptive properties possessed by all members of an entity set.
Domain – the set of permitted values for each attribute Attribute types:
Simple and composite attributes. Single-valued and multi-valued attributes
Example: multivalued attribute: phone_numbers Derived attributes
Can be computed from other attributesExample: age, given date_of_birth
Example: customer = (customer_id, customer_name,
customer_street, customer_city )loan = (loan_number, amount )
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Composite Attributes
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Mapping Cardinality Constraints
Express the number of entities to which another entity can be associated via a relationship set.
Most useful in describing binary relationship sets. For a binary relationship set the mapping cardinality must be
one of the following types: One to one One to many Many to one Many to many
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Mapping Cardinalities
One to one One to many
Note: Some elements in A and B may not be mapped to any elements in the other set
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Mapping Cardinalities
Many to one Many to many
Note: Some elements in A and B may not be mapped to any elements in the other set
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Keys
A super key of an entity set is a set of one or more attributes whose values uniquely determine each entity.
A candidate key of an entity set is a minimal super key Customer_id is candidate key of customer account_number is candidate key of account
Although several candidate keys may exist, one of the candidate keys is selected to be the primary key.
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Keys for Relationship Sets
The combination of primary keys of the participating entity sets forms a super key of a relationship set. (customer_id, account_number) is the super key of depositor NOTE: this means a pair of entity sets can have at most one
relationship in a particular relationship set. Example: if we wish to track all access_dates to each account by each
customer, we cannot assume a relationship for each access. We can use a multivalued attribute though
Must consider the mapping cardinality of the relationship set when deciding the what are the candidate keys
Need to consider semantics of relationship set in selecting the primary key in case of more than one candidate key
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
E-R Diagrams
Rectangles represent entity sets. Diamonds represent relationship sets. Lines link attributes to entity sets and entity sets to relationship sets. Ellipses represent attributes
Double ellipses represent multivalued attributes. Dashed ellipses denote derived attributes.
Underline indicates primary key attributes (will study later)
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
E-R Diagram With Composite, Multivalued, and Derived Attributes
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Relationship Sets with Attributes
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Roles
Entity sets of a relationship need not be distinct The labels “manager” and “worker” are called roles; they specify
how employee entities interact via the works_for relationship set. Roles are indicated in E-R diagrams by labeling the lines that
connect diamonds to rectangles. Role labels are optional, and are used to clarify semantics of the
relationship
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Cardinality Constraints
We express cardinality constraints by drawing either a directed line (), signifying “one,” or an undirected line (—), signifying “many,” between the relationship set and the entity set.
One-to-one relationship: A customer is associated with at most one loan via the relationship
borrower A loan is associated with at most one customer via borrower
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
One-To-Many Relationship
In the one-to-many relationship a loan is associated with at most one customer via borrower, a customer is associated with several (including 0) loans via borrower
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Many-To-One Relationships
In a many-to-one relationship a loan is associated with several (including 0) customers via borrower, a customer is associated with at most one loan via borrower
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Many-To-Many Relationship
A customer is associated with several (possibly 0) loans via borrower
A loan is associated with several (possibly 0) customers via borrower
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Participation of an Entity Set in a Relationship Set
Total participation (indicated by double line): every entity in the entity set participates in at least one relationship in the relationship set E.g. participation of loan in borrower is total
every loan must have a customer associated to it via borrower Partial participation: some entities may not participate in any relationship in
the relationship set Example: participation of customer in borrower is partial
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Alternative Notation for Cardinality Limits
Cardinality limits can also express participation constraints
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
E-R Diagram with a Ternary Relationship
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Cardinality Constraints on Ternary Relationship
We allow at most one arrow out of a ternary (or greater degree) relationship to indicate a cardinality constraint
E.g. an arrow from works_on to job indicates each employee works on at most one job at any branch.
If there is more than one arrow, there are two ways of defining the meaning. E.g a ternary relationship R between A, B and C with arrows to B and C
could mean 1. each A entity is associated with a unique entity from B and C or 2. each pair of entities from (A, B) is associated with a unique C entity,
and each pair (A, C) is associated with a unique B Each alternative has been used in different formalisms To avoid confusion we outlaw more than one arrow
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Design Issues
Use of entity sets vs. attributesChoice mainly depends on the structure of the enterprise being modeled, and on the semantics associated with the attribute in question.
Use of entity sets vs. relationship setsPossible guideline is to designate a relationship set to describe an action that occurs between entities
Binary versus n-ary relationship setsAlthough it is possible to replace any nonbinary (n-ary, for n > 2) relationship set by a number of distinct binary relationship sets, a n-ary relationship set shows more clearly that several entities participate in a single relationship.
Placement of relationship attributes
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Binary Vs. Non-Binary Relationships
Some relationships that appear to be non-binary may be better represented using binary relationships E.g. A ternary relationship parents, relating a child to his/her father
and mother, is best replaced by two binary relationships, father and motherUsing two binary relationships allows partial information (e.g. only
mother being know) But there are some relationships that are naturally non-binary
Example: works_on
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Converting Non-Binary Relationships to Binary Form
In general, any non-binary relationship can be represented using binary relationships by creating an artificial entity set. Replace R between entity sets A, B and C by an entity set E, and three
relationship sets:
1. RA, relating E and A 2.RB, relating E and B3. RC, relating E and C
Create a special identifying attribute for E Add any attributes of R to E For each relationship (ai , bi , ci) in R, create
1. a new entity ei in the entity set E 2. add (ei , ai ) to RA
3. add (ei , bi ) to RB 4. add (ei , ci ) to RC
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Converting Non-Binary Relationships (Cont.)
Also need to translate constraints Translating all constraints may not be possible There may be instances in the translated schema that
cannot correspond to any instance of RExercise: add constraints to the relationships RA, RB and RC to
ensure that a newly created entity corresponds to exactly one entity in each of entity sets A, B and C
We can avoid creating an identifying attribute by making E a weak entity set (described shortly) identified by the three relationship sets
Computing & Information SciencesKansas State UniversityWednesday, 19 Sep 2007CIS 560: Database System Concepts
Weak Entity Sets
An entity set that does not have a primary key is referred to as a weak entity set.
The existence of a weak entity set depends on the existence of a identifying entity set it must relate to the identifying entity set via a total, one-to-many
relationship set from the identifying to the weak entity set Identifying relationship depicted using a double diamond
The discriminator (or partial key) of a weak entity set is the set of attributes that distinguishes among all the entities of a weak entity set.
The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent, plus the weak entity set’s discriminator.