e-commerce jobs this project (project number: hu/01/b/f/pp-136012) is carried out with the financial...

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E-COMMERCE JOBS This project (Project number: HU/01/B/F/PP-136012) is carried out with the financial support of the Commssion of the European Communities under the Leonardo da Vinci Programme

Database ModelsVer: 1.0

E-Commerce Databases

Database models

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Relational Databases

• Entities (e.g. Customer, Products ...)• Relationships (e.g. a Customer orders many

Products)• Entity Relationship Diagram (ERD)• Normal Forms (to exclude duplicity of data and

resulting update problems)

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Entity Type / Table

• Tables• Attributes• Records

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Primary Keys

• Primary Keys• Relationships

Primary Key cus_id

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Relationships

Customer Productconfirms sales

n:m

Customer Productconfirms

sales1:n

sold

n:1

Relationshipsbecome Tables

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Relationships

Customer Table

SalesTable

ProductTable

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Entity Relationship Diagram

• Illustrating entity types and their relationships• Input for the database design team which tables

to create

Customer Productconfirms

sales1:n

sold

n:1

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Redundancy Elimination

• First Normal Form– First Normal Form eliminates repeating groups by putting each into a separate table and

connecting them with a one-to-many relationship.

• Second Normal Form– Second Normal Form eliminates functional dependencies on a partial key by putting the

fields in a separate table from those that are dependent on the whole key.

• Third Normal Form– Third Normal Form eliminates functional dependencies on non-key fields by putting them in a separate

table. At this stage, all non-key fields are dependent on the key, the whole key and nothing but the key.

-> Data are normalised !

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1Nf to 2NF Example

• Separate into different entities/tables• Check that no attributes are dependent on key-subset (e.g.

warehouse-address being dependent on key warehouse)

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2NF to 3NF Example

• Identify non-key fields which would be keys of a separate table• Separate out these tables

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4NF / 5NF

Employee

Language

Competence1:n n:1

Skill

1:n

employee_id, skill_id, lang_id

Speaking

Capability

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Exercise 1 Master Example 1

• Design the Entity Realtionship Diagram for a typical customer and product sales situation including stock control

• Identify the primary keys, the relationships, and the attributes required within each table

• Check against the 3NF• Do this work in about 1 hour

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Exercise 2 Master Example 2

• Design the Entity Realtionship Diagram for a typical e-newspaper ordering site with customers, newspapers to select, newspapers to renew and to administer sales and payments

• Identify the primary keys, the relationships, and the attributes required within each table

• Check against the 3NF• Do this work in about 1 hour

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References

• F. Codd, "A Relational Model of Data for Large Shared Data Banks", Comm. ACM 13 (6), June 1970, pp. 377-387. The original paper introducing the relational data model.

• F. Codd, "Normalized Data Base Structure: A Brief Tutorial", ACM SIGFIDET Workshop on Data Description, Access, and Control, Nov. 11-12, 1971, San Diego, California, E.F. Codd and A.L. Dean (eds.). An early tutorial on the relational model and normalization.

• E.F. Codd, "Further Normalization of the Data Base Relational Model", R. Rustin (ed.), Data Base Systems (Courant Computer Science Symposia 6), Prentice-Hall, 1972. Also IBM Research Report RJ909. The first formal treatment of second and third normal forms.

• C.J. Date, An Introduction to Database Systems (third edition), Addison-Wesley, 1981. An excellent introduction to database systems, with emphasis on the relational.

• R. Fagin, "Multivalued Dependencies and a New Normal Form for Relational Databases", ACM Transactions on Database Systems 2 (3), Sept. 1977. Also IBM Research Report RJ1812. The introduction of fourth normal form.

• R. Fagin, "Normal Forms and Relational Database Operators", ACM SIGMOD International Conference on Management of Data, May 31-June 1, 1979, Boston, Mass. Also IBM Research Report RJ2471, Feb. 1979. The introduction of fifth normal form.

• W. Kent, "A Primer of Normal Forms", IBM Technical Report TR02.600, Dec. 1973. An early, formal tutorial on first, second, and third normal forms.

• T.-W. Ling, F.W. Tompa, and T. Kameda, "An Improved Third Normal Form for Relational Databases", ACM Transactions on Database Systems, 6(2), June 1981, 329-346. One of the first treatments of inter-relational dependencies.

e-commerce jobs this project (project number: hu/01/b/f/pp-136012) is carried out with the financial...

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