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  1. 1.  Data codes have two purposes: 1) Uniquely identify an entity or identify an entity as a member of a group or set. 2) Identification purposes, codes often are more compact than textual or narrative description because they require fewer characters to carry a given amount of info.
  2. 2.  Addition: An extra character is added to the code Truncation: a character is omitted. Transcription: a wrong character is recorded. Transposition: Adjacent characters of the code are reversed. Double transposition: characters separated by one or more characters are reversed.
  3. 3.  Length of the code: Longer codes are more error prone. They should be broken into chunks by using hyphens, slashes, or spaces. Alphabetic / numeric mix: if alphabetic and numeric characters are mixed in a code, error rate is lower if alphabets are grouped together and numeric are grouped together.
  4. 4.  Choice of characters: If possible, the characters B,I,O,S,V,Z should be avoided because they frequently confuse with characters 8,1,0,5,U, and 2. Mixing uppercase/lowercase fonts: Having to use the shift key during keying of a code breaks the rhythm and increases the likelihood of error. Special characters like @,*,# also cause problem. Predictability of character sequence: some character sequences are more predictable than others and as such, are less error prone.
  5. 5.  Serial codes: assign consecutive numbers(or alphabetic) to an entity, irrespective of the attributes of the entity. Advantage: Ease of addition of new item and conciseness. Different users might wish to view data differently. A code that presumes one view of data might be inappropriate for certain users. Disadvantage: Creates problem when file of item is volatile-i.e significant no. of addition and deletion occur.
  6. 6. block sequence codes: assignblocks of numbers to particular categoryof an entity. Primary attribute on whichentities are to be categorized must bechosen. And blaocks of numbers mustbe assigned to customers on the basis ofthe discount allowed each customer. Advantage: have the advantages ofgiving some mneumonic value to thecode. Disadvantage: difficult to choose sizeof the block needed.
  7. 7.  Hierarchical codes: Require selection of the set of attributes of the entity to be coded and their ordering by importance. The value of code is a combination of the value of the codes for each attribute of the entry. Advantage: Describe more attributes of the entity which they apply. Disadvantage: Not always concise. They mix alphabets and numerics, which undermine recall accuracy.
  8. 8.  Association codes: attributes of the entity to be coded are selected. and unique codes are then assigned to each attribute value. Codes can be numeric alphabetic or alphanumeric. The code for the entity is simply the concatenation of the different codes assigned to the attributes of the entity.