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| Newer page: | version 3 | Last edited on Wednesday, September 10, 2003 10:56:48 pm | by StuartYeates | |
| Older page: | version 2 | Last edited on Wednesday, September 10, 2003 10:52:48 pm | by CraigBox | Revert |
@@ -5,9 +5,9 @@
A secondary key is a non-strict subset of the columns of any table that correspond to the primary key of another table.
A relation differs from a SpreadSheet in that the rows and columns are unordered.
-[SQL] set-oriented is a language designed to build, maintain and query such [DataBase]s.
+[SQL] set-oriented is a language designed to build, maintain and query such [DataBase]s. Because of the very clean mapping of tables and rows into set theory a large number of properties about relational databases have been proved in a mathematical sense and automatic query optimisation is now a standard option on many high-end relational databases. There are also formal proofs of correctness for a number of results in for locking relational databases at various levels of granularity, permitting parallel access
.
RelationalDataBase quality revolves around five normal forms:
#__first normal form__ requires that no relation have multiple-valued fields.
#__second normal form__ requires __first normal form__ and that no non-primary key fields are independant of any primary key fields.
@@ -16,5 +16,5 @@
#__fifth normal form__ requires __fourth normal form__ and that relations cannot be decomposed into smaller realtions without loss of information.
These aren't very good explainations, but I didn't want to cut and paste. There are very large number of books and websites on relational database design.
-There are very few real-world [RelationalDataBase]s, most of the databases which we thing of
as [RelationalDataBase]s ([Oracle], [MySQL], [PostgreSQL] and [DB2])
are actually [PostRelationalDataBase]s.
+There are very few real-world [RelationalDataBase]s, most of the databases marketed
as [RelationalDataBase]s are actually [PostRelationalDataBase]s.
