Understanding The Principles Of Direct Manipulation In A DBMS Environment

The principles of direct manipulation in a dbms environment are given as follows:

 

- Continous, visual representation of the object of interest.
- Physical mechanisms, instead of complex language syntax, to position a cursor and manipulate the object.
- Rapid, incremental operations immediately display the effect of the action

Video games provide and exciting, well engineered and certainly successful illustration of direct manipulation. The users know the precise point or object which is to be manipulated and they see an immediate response to their directives. The strong attraction of these games contrasts markedly with the anxiety and resistance many users experience toward office automation equipment.

Continous, visual representation of the object of interest:

Some representation of the object the user is currently viewing or manipulating should always be visible on the display device. The user should also be able to see immediately the effect of any operations or modifications on the object of interest. The chosen representation should be natural and lead to unambiguous interpretation by the population of intended users. The use of a graphic icon may be clear to a designer but may lead to a greater confusion.

A graphic representation may be an analogy which leads the user to make incorrect assumptions about permissible operations on the object. Within a dbms, the objects to be represented include records, data item values which make up a record and relationships between records. The system could display a data structure graphically showing data files as boxes or file drawers and relationships as arcs between boxes. Different arcs could represent relationships with different characteristics.

The user could move over the structure to select the file and relationships of interest. Within a file, the system could graphically portray thumbing through the entries or records in a file by displaying overlapping boxes or file folders with the search keys written across the top of each folder. The user would be able to move back and forth through the file, deleting records, and opening up a record for closer examination and possible update or tagging records for further collective action on the tagged set or the untagged set. Before moving through the file, the user could specify which key or keys to search on, which data items to display on the top of each folder and which records to include in the scan.

 

Physical Actions instead of complex language syntax:

When users must write a command statement in some language to direct the actions of a system, they must first learn the command structure, semantics and syntax of the language. They must learn how to put the command sequences together to perform a particular task. They must also write the commands correctly or risk getting a syntax error. The amount of initial learning required before using the system is a significant barrier to acceptance and use.

Furthermore the syntax of languages tends to be somewhat arbitrary, as in selecting the keys of letters to invoke particular actions. While some designers try to choose command letters for the mnemonic value, inconsistencies across systems are inevitable and annoying. Syntactic knowledge is acquired through rote memorization, making it easily forgotten unless frequently used. The solution is to utilize physically obvious and naturally intuitive mechanisms for positioning and labeled buttons for actions.

 

Rapid, Incremental operations immediately visible:

After performing an operation, users ought to be able to see the effects immediately on the screen. They should not have to wait for the system to redisplay or repaint the whole screen. They certainly should not have to explicitly request a display or print to see and verify the effect of the operation. Errors are immediately apparent. Inserting characters in a data value should be possible without retyping the whole value. The existing characters would be shifted over as the new characters were ordered.

Deleting characters from a string, the system would shift the remaining characters to fill in the space. After deleting a line, the system would move the subsequent lines up. Operations should be easily reversible. Typing mistakes can be easily corrected by backspacing and retyping or deleting an extraneous character. An UNDO command key could return the system to the state prior to the previous command. Easy reversibility, using natural inverse operations or UNDO, is essential to reducing user anxiety about making mistakes or destroying some data.

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