ICS 121: Design Specialties

What specific misuses are you trying to prevent?
Prevent misuse at every access layer:
- Physical access to the machines and backup tapes
- Network addresses, routers, and wiring
- Operating system accounts and services
- Application code
Authentication: how do you know that the user is the person that they claim to be?
Authorization: what is this user allowed to do?
Encryption: can anyone else intercept communications?
Auditabiliy: Can you review how the system was used and detect any misuse? Can you recover from misuse?

There are many kinds of reuse: any differnt artifact can be reused, including requirements documents, design documents, and code.
It takes more work to make a component more broardly reusable: better documentation, support for more use cases, better error handling.
Reuse saves time and effort in the long-run: more work, but shared among more projects that use the component over time.
Reuse is most successful when there is a community of users that can support each other and make modifications over time.
Reuse can be opportunistic or planned.
- Opportunistic reuse happens by chance: you create a reusable component and hope that someone will reuse it someday.
- Planned reuse happens within the context of a product line within a company. You have some idea of who will reuse the code and when, and what specific capabilities they will need.

Scalability is the ablity of your product to handle more difficult inputs. E.g., process longer input files, or handle input from more users at the same time.
Before you can talk about scalability, you must define the input parameter that is being scaled. E.g., number of concurrent users. E.g., number of bytes in the input file.
One way to improve scalability is to use more efficient datastructures and algorithms. E.g., no Bubblesort.
Another way to improve scalability is to deploy components across multiple machines and load-balance between them. E.g., Yahoo.com has many many web server machines.

UI design is a complex topic that requires study and practice to do well.
One good piece of advice for non-experts is to simply make their new products imitate other products that have been used by the target audience. E.g., if you are designing a new spreadsheet, make the UI similar to MS Excel, because your customers probably know Excel.
When designing a user interface:
- Start by understanding the tasks that the user must accomplish. Use use cases and low-fidelity mockups
- Address screen layout, widget choice, and presentation last
UI consistency
- The most important type of consistency is a good match between the user's task and the use cases supported by the product.
- Your product should be consistent with published UI guidelines and the UIs of other popular products.
- Your product should be internally consistent: e.g., use the same label for the same button even if it appears in more that one dialog box.
Evaluate your use cases and use UI design checklists. Have a few users try the product and give you feedback. Do not try to conduct a large-scale user study unless you are trained to do that.

"Persistence" means the storage of data to persistent media, such as a file on a harddisk. Persistence also includes database design.
Can your database or file accurately represent everything that needs to be stored? Enough flexibility? Enough capacity?
Is your database or file format easy and efficient to access and update? Even when it holds a large amount of data?
What access controls should be placed on the files or database?
For any new file formats, try using XML before considering any other approach.