Here are some online sites with useful database management concepts and tips including some good discussion of database normalization: and first, second, and third normal form: (In particular, PHPBuilder has understandable examples of the different levels of normalization.) Third Normal Form prohibits transitive dependencies whereby a non-key attribute is dependent on another non-key attribute (e.g., only put a unique owner ID in the parcel table and not any other owner information such as their age or mailing address). Second Normal Form requires that non-key fields must be dependent upon the entire key (e.g., don't put the owner name as well as an owner ID in the parcel table). First normal forms requires that there be no multi-valued attributes (e.g., for the URISA database, do not put multiple keyword codes in the same cell, and do not have keyword1, keyword2, etc. With fewer columns - after conducting some tests and applying some rules. Normalization generally involves taking a design withДЇewer tables and many columns and transforming it into a design with more tables Normal forms, Third Normal Form is generally considered good enough for Much of formal database design is focused on normalizing the databaseДЄnd ensuring that the design conforms to a level of normalization (e.g.,ДЇirst normal form, second normal form, etc.). Commercially available tools can automate the process of converting a E-R.These foreign keys shouldД«e included in the third table's primary key, if appropriate That has foreign keys that refer to the entities in each original table. Many-to-many relationships among two entities are modeled by defining a third table.Table representing the entity on the 'many' side of the relationship (e.g., theДЇIRES table has a foreign key that refers to the PARCELS table)

One-to-many relationships are modeled by a foreign key attribute in the.Each remaining entity is modeled by a table with a primary key and attributes,.Entities with one-to-one relationships can (and often should) be merged into a single entity.Define the relationships between primary keys in one table and foreign keys in another.Define the (unique) primary key of each entity.Determine the attributes of each entity.Many-to-many (e.g., parcel sales: a parcel may be sold many times by different owners,ДЄnd an individual owner may sell many parcels).One-to-many (e.g., a parcel may be involved in many fires).One-to-one (e.g., a parcel has one address).Determine the cardinality relationships among the entities and classify.Identify the entities that your database must represent.It is drawnД«y importing the tables from Oracle to MS-Access and then using the Tool/RelationshipsД¬apability of MS-Access to draw the diagrams: Here's an ER diagram of portions of the 'parcels' test database.Result of the process is a normalized database that facilitates.Entities have relationships with one another.An entity is a class of distinct identifiable objects or concepts.Represents the data by entities that have attributes.Entity-Relationship (E-R) Modeling: A method for designing databases.Introduction to Entity-Relationship Modeling Note: These objectives are sometimes contradictory!.Clean, consistent, and easy to understand.Supports the maintenance of data integrity over time.Can represent all expected data over time.Reflects real-world structure of the problem.Such an included column is called a foreign key A table is linked to another by including the other table's primary key.Most primary keys are a single column (e.g., OWNERNUM for OWNERS).Each table has a primary key, a unique identifier constructed from.A proper relational table contains no duplicate rows.Rows are (officially) unordered (i.e., the order in which rows are referenced.Tables are comprised of rows and columns (tuples).All data are represented as tables (relations).Updates - examples of UPDATEs only for SELECTed rows] Review: The Relational Introduction to Relational Database Design (based on Lecture by Tom Grayson)Д®nforcing Referential Integrity in Oracle

Referential Integrity and Relational Database Design

Free relational database design tool