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Replicator Plus


This essay does not describe an existing computer program, just one that should exist. This essay is about a suggested student project in Java programming. This essay gives a rough overview of how it might work. I have no source, object, specifications, file layouts or anything else useful to implementing this project. Everything I have prepared to help you is right here.

This project outline is not like the artificial, tidy little problems you are spoon-fed in school, when all the facts you need are included, nothing extraneous is mentioned, the answer is fully specified, along with hints to nudge you toward a single expected canonical solution. This project is much more like the real world of messy problems where it is up to you to fully the define the end point, or a series of ever more difficult versions of this project and research the information yourself to solve them.

Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; or give you any additional materials. I have too many other projects of my own.

Though I am a programmer by profession, I don’t do people’s homework for them. That just robs them of an education.

You have my full permission to implement this project in any way you please and to keep all the profits from your endeavour.

Please do not email me about this project without reading the disclaimer above.

The Problem

People often ask me if they can mirror some of the material on my website. I would probably say yes if they wanted to translate it into another language. I would probably say yes if they wanted to use it in a magasine article. I usually say no for general mirroring because there is no technology to ensure those clones up-to-date.

As a first cut solution to this problem, I wrote the Replicator, which maintains a mirror copy of my entire website by sending any deltas (recent changes) that the client does not yet have and have not been superceded.

There are several problems with this solution:

Your Mission

Your mission, if you choose to accept it, is to solve this problem.

How Might It Work

The client highlights something they want to borrow from your website. Client-side code asks the server for a laundry ticket to retrieve that chunk of html expanded to next bigger logical boundary. The client side code saves the laundry ticket to hard disk, but not necessarily the text.

This laundry ticket embedded in HTML (Hypertext Markup Language), suitably sandwiched, will send a probe to my server and retrieve the text (possibly changed) for the laundry ticket and display that markup.

There is also an application to let you view and organize (i.e. delete junk in the database of laundry tickets). T Cache the text for laundry tickets. Decide whether you want to support Ctrl-C. Either way is unacceptable to some.

You database works first to check the most recent updates of various laundry tickets. If they are out-of-date, any cached value is logically deleted.

This a quite different program from the Replicator, though there is some common logic.

Aquarium Sand Depth Calculator
Raspberry π

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