Hotspots: Admin Pages | Turn-in Site |
Current Links: Cases Final Project Summer 2007
CoWeb Assignment 3 (7/28)
History of OO (1 point)
What was the first object-oriented language? What two elements, kept separate in structured programming, did it combine?
Simula. The 2 elements were data and functions (or procedures).
Name three contributions to computing that were made at the learning research group at Xerox PARC?
Those 3 contributions were graphic user interfaces (GUIs), the Ethernet, and What You See Is What You Get (WYSIWYG) technology.
Usability (1 point)
Don Norman provides a simple framework for explaining the interaction between people and the physical world. As part of that framework, he identifies two “gulfs”: the gulf of evaluation and the gulf of execution. Describe these and provide an example of each gulf in a situation of a user interacting with a computer application.
Norman describes the problem writers and designers face in meeting the goals of users as two gulfs between the user and the system.
The Gulf of Execution represents the difficulty the user has in translating a psychological goal into a physical action. For example, the goal "learn more about avocados" is purely psychological. The user of a hypertext system on the WWW will need to see the available links, recognize the appropriate choice, and use the mouse to point and click on that link. Thus, in order to learn more about avocados, the user needs to execute a set of physical steps.
The Gulf of Evaluation represents the user's difficulty in evaluating whether the response of the computer system meets the desired goal. In the above example, the user would need to perceive the system response, examine the resulting node, and assess whether it presented the proper information about avocados. In the same way that the user needed to translate a psychological goal into a physical action sequence to bridge the Gulf of Execution, the user needs to compare the physical response of the system against the psychological goal to bridge the Gulf of Evaluation.
Garbage Collection (1 point)
Reference counting was one of the first implementations of garbage collection. Ultimately, it proved problematic. Why?
With reference counting, one drawback of this system is that each block of memory allocated must have sufficient space available to maintain its reference count. However a more serious problem is the existence of circular lists. Even if nothing else points to the circular list, each item of the list will have another item of the list pointing to it.
Name two advantages and one disadvantage to using garbage collection.
The advantages include automating memory allocation and freeing, and eliminating errors that would have occurred due to mistakes related to memory allocation. One disadvantage is that it can potentially worsen performance because time can be wasted while the garbage collector scans the heap for things no longer needed.