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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