Thursday, October 22, 2009
Relational Databases
Relational databases are the most common type of databases used today. The main reason for its popularity is the fact that relational database systems allow users to view the database in a logical rather than a physical way. This eliminates the need for users to understand the underlying details of how the data is stored. The relational database uses tables (relations). How are relational databases able to use tables to create relationships? Why do we need a unique identifier in each table? Suppose we are the design the library database at UGBC, how many (main) tables might we need? What are the main tables? How can we set up the relationships among the different tables.
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- Relational databases are able to use tables to create relationships since tables are created to logical group the entities for the data in order to have them organized so to allow easy access and retrieval. Relationships are created between the tables since the tables will have related entites thus forming relations between two or more tables. This makes the database more efficient.
ReplyDelete- A unique identifier or primary key makes each record unique which ensures there are no duplicates in the records.
- Main tables may include:
. Books
. Authors
. Category
- The relationships:
. there may be a one-to-many relationship between the authors and the books, since an author may write several books.
. Also a one-to-many relationship between category and books, since each category will have several books belonging to it.
. There may also be a one-to-many relationship existing between category and authors, which provides that several authors write a particular category of books.
relational database used tables to create relationship by linking the tables by a unique entity.that entity is known as the primary key.we need a unique identifier to difference between tables .it makes the table unique so that there is no duplicate table and it also eliminate redundant information.
ReplyDeletetwo other main table should be added to the previous answer-journal and student.
the relationship must be set up among the tables as either a one-to-one or a one-to-many relationship.each table must have a primary key and also a foreign key.both keys established the relationship between the tables.
there is a one -to-many relationship between students and books as a student can borrow many books but one book of the same ttile can only borrow by one student.