Remove Duplicates from arrary .net
First Normal Form
no repeating groups
Eliminate duplicative columns from the same table.
Create separate tables for each group of related data and identify each row with a
unique column (the primary key).
An entity is in the first normal form if it contains no repeating groups. In relational
terms, a table is in the first normal form if it contains no repeating columns. Repeating
columns make your data less flexible, waste disk space, and make it more difficult to search
for data. In the telephone directory example in Figure 19, it appears that the name table
contains repeating columns, child1, child2, and child3.
Figure 19. Name Entity Before Normalization
You can see some problems in the current table. The table always reserves space on the disk
for three child records, whether the person has children or not. The maximum number of
children that you can record is three, but some of your acquaintances might have four or
more children. To look for a particular child, you have to search all three columns in every
To eliminate the repeating columns and bring the table to the first normal form, separate
the table into two tables as Figure 20 shows. Put the repeating columns into one of the
tables. The association between the two tables is established with a primary-key and
foreign-key combination. Because a child cannot exist without an association in the name
table, you can reference the name table with a foreign key, rec_num.
Second Normal Form (2NF)
Remove subsets of data that apply to multiple rows of a table and place them in separate
Create relationships between these new tables and their predecessors through the use of
Third Normal Form (3NF)
There are two basic requirements for a database to be in third normal form:
Already meet the requirements of both 1NF and 2NF
Remove columns that are not fully dependent upon the primary key.
Fourth Normal Form (4NF)
Finally, fourth normal form (4NF) has one additional requirement:
Meet all the requirements of the third normal form.
A relation is in 4NF if it has no multi-valued dependencies.
Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it
must first fulfill all the criteria of a 1NF database.
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The manipulation includes displaying, adding, editing, and deleting data from a single XML file using C#.