The Object-Action (or visa-versa) model and its applications
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Contents |
Background
Object Action Interface or Action Object Interface is changing the way people interact with systems. As more and more systems switch from text mode command based languages to Graphical User Interface (GUI) the problem now lies with visually representing and displaying of user's tasks objects and actions. Before GUI was implemented in systems and users had to remember a set of commands and if they ever had to use a command which was not used frequently they would have to refer to another user of the manual pages.
Object Action Interface is basically an extension to the Graphical User Interface, it also relates to Direct Manipulation User Interface. DMUI can help create better Human Computer Interfaces and can also increase the usability of the product
There are two basic interaction models for any given system.
Object Action Interface
In this model the user will select the object first and then select the action which will be performed on the object.
Example: In Windows, if you want to copy a file you will first select a file (Object) and then right click and select copy (Action).
Action Object Interface
In this model the user will select an action and then select the object the action will be performed on.
Example: In command prompt, if you want to copy a file you will input copy <Source File> <Destination File>. 'Copy' which is the action comes before the object '<Source File>'
Scope
There has always been distinction between those two models in several domains starting long ao by compiler designers who always wanted to distinguish between syntax, which is different tokens parsed from a source code file, and the semantics, which are the actual operations invoked by that text. Different areas use the syntactic-semantic model of human behaviour, such as programming, database manipulation facilities and direct manipulation (Shneiderman, 1980, 1981)
Example
The difference between the two models can be seen when comparing a command based system (UNIX) to a GUI environment (Windows). The task to copy or move a file from one directory in UNIX is different than in Windows. In UNIX the action of copying is specified first and then object. In Windows the object is first selected then the action of copying is applied.
The Object Action Model is also used in a real life environment. If you want to move a file from one folder to another you will first select the file and then move it. You cannot choose the action of moving and then select the file.
Principles
OAI Model
Syntactic Knowledge
Task hierarchies of objects and actions
Tasks are composed of objects and actions at high and low levels. Not all users will find these hierarchies to be perfect, but since they are comprehensible, a great deal of usefulness is provided.
User
Dividing complex tasks into sub-tasks and solving the sub-tasks independently has been shown to be a successful way to solve larger complex problems. Most real world objects and entities involve the use of this property of creating sub-tasks to create a plan of smaller action steps. People learn tasks actions and objects within their lifetime and realize that the process is simplified greatly, when managing different smaller levels within a hierarchy. Issues of implementation are not considered as much when executing tasks using this method.
Designer
Three steps are suggested by Ben Shneiderman, the creator of the 8 golden rules of interface design, for designers to correctly build a task hierarchy.
1. Know about the users and their tasks (Interviewing users, reading workbooks and taking training sessions) 2. Generate hierarchies of tasks and objects to model the users' tasks 3. Design interface objects and actions that metaphorically map to the real world universe
Interface hierarchies of objects and actions
This hierarchy is similar to task hierarchy, since it also contains hierarchies of objects and tasks at different levels.
Interface Objects
Users that interact with a computer system are exposed to high level concepts relevant to that system. These high level concepts include, but are not limited to: files, menus, buttons, pop-up boxes etc.. They acquire exposure to the properties of the objects and how manipulation of its properties can shape the use of the object. Through this experience, they achieve a basic understanding of how to perform actions and accomplish the tasks.
Interface Actions
These are also hierarchies of lower levels actions which can be performed of objects relevant to the domain of computers as set out in the interface objects hierarchy. There are three levels of decomposition within the hierarchy. A high level plan might be to create a text file, which could involve mid-level actions such as creating a file, inserting text into that file and saving that file. The mid level action of saving the file can be decomposed into lower level actions like creating a backup copy and setting the access control rights of that file. More lower level actions might include naming the file, the location the file is stored, and dealing with errors such as space shortage, font, layout, etc.
User
Users can learn interface objects and actions in several different ways such as demonstrations, sessions or trail and error sessions. Once these objects and actions depict a logical structure that the user can relate to other tasks objects and actions, the user more likely to remember and implement this knowledge in the future.
Designer
Designers use the OAI model to understand the complexity of the processes that the user has to perform in order to successfully use an interface to perform a certain task. Designers model the interface actions and objects based on familiar examples and then adjust and fine tune these models to fit the task and the user.
Limitations and Challenges
Metaphor Interpretation
Each user's way of performing a task may vary. Defining steps completely with metaphors creates risk in the varying interpretations of metaphors amongst different users. Designers of object-action models must consider the wide range of interpretations that are possible when deciding on metaphors for an object. If there is a serious difference between the designer's interpretation and the user's interpretation of the metaphor used, the meaning of the model will be lost. In this case, all the work done to create the model will be lost and the user will be unable to perform the desired task with the interface.
Batching and Pipelining
Users of UNIX and other command line based systems may find that their usual actions of
References
- Amir Khella, Object Action Interface Model
