Lab 8 - Getting Sociable with Perl
Overview
In this lab, we'll write the database backend for a very simple social network application. This application will only worry about keeping track of lists of people's friends, where friendship is automatically mutual - if Alice is friends with Bob, then Bob is friends with Alice as well. We'll also review the solution to the lab from last week.

 

Last week's lab
Last week's lab was a (relatively) simple extension of previously-written code that required you to import a few functions into your new program (using a require statement, not copy+paste) and then call them in a loop. The code that you had to write was almost exactly the same as the code in the solution developed in the first part of the lab, except that it happened in a loop. We'll go over the solution in lab - if you don't understand something, there are probably four other people who don't either and would be secretly grateful to you if you stopped me and asked.

 

Social Networking

Imagine you want to create a better Facebook (much of which is written in Perl, by the way). The first step would be to create a database that keeps track of users and their friends. We'll write a simple program to demo this database. If you were really creating a better Facebook, you might use the methods you create here as part of a much larger program; in this lab, we'll develop them with modularity in mind.

Here is a example of how your program might look when run. In this example, I become friends with my evil twin but then remove the friendship when I realize his sinister secret. 

jpr@sulu (i211/lab8) % ./socialnet.pl add Jacob Ratkiewicz
jpr@sulu (i211/lab8) % ./socialnet.pl add Bocaj Zciweiktar
jpr@sulu (i211/lab8) % ./socialnet.pl print
Jacob Ratkiewicz has no friends.
Bocaj Zciweiktar has no friends.
jpr@sulu (i211/lab8) % ./socialnet.pl friend Jacob Ratkiewicz Bocaj Zciweiktar
jpr@sulu (i211/lab8) % ./socialnet.pl print
Jacob Ratkiewicz is friends with:
        Bocaj Zciweiktar
Bocaj Zciweiktar is friends with:
        Jacob Ratkiewicz
jpr@sulu (i211/lab8) % ./socialnet.pl add Random Dude
jpr@sulu (i211/lab8) % ./socialnet.pl friend Jacob Ratkiewicz Random Dude
jpr@sulu (i211/lab8) % ./socialnet.pl print
Bocaj Zciweiktar is friends with:
        Jacob Ratkiewicz
Jacob Ratkiewicz is friends with:
        Bocaj Zciweiktar, Random Dude
Random Dude is friends with:
        Jacob Ratkiewicz
jpr@sulu (i211/lab8) % ./socialnet.pl unfriend Jacob Ratkiewicz Bocaj Zciweiktar
jpr@sulu (i211/lab8) % ./socialnet.pl print
Jacob Ratkiewicz is friends with:
        Random Dude
Bocaj Zciweiktar has no friends.
Random Dude is friends with:
        Jacob Ratkiewicz


Notice that the program socialnet.pl is being run from the command line multiple times, but somehow remembers who is friends with who between each run. That is because it is using a hash tied to a DB_File (really, to an MLDBM) to remember friendship relations. That's hint #1. Hint #2, even more important, is that this is exactly what you need to do in Project Checkpoint 2.

Do this:

Start writing socialnet.pl. Remember, the first step is to understand what needs to be done and to break it down into subroutines. I will help you with this step. The next step is to start writing subroutines. Remember, you'll be happiest and healthiest if you write subroutines in the order that makes them easiest to test. What subroutine should you write first? Second?

Your program should recognize the following commands, given on the command line:

  • add Firstname Lastname - Add someone named "Firstname Lastname" to the database, initially with no friends.
  • friend Some Guy Random Person - Creates a friendship link between "Some Guy" and "Random Person", and vice-versa (since friendship is mutual).
  • unfriend Some Guy Random Person - Removes the link "Some Guy"->"Random Person", and vice-versa.
  • print - Print the current state of the friendship database - who's inside, and who their friends are.

You can assume that your users give you valid input. Here are some links that might help:

 

Turn in your assignment

Strictly speaking, there's only one file in this week's lab, so a tarball isn't really required. However, let's make one anyway.

As a reminder, here's the command you can use:

jpr@sulu (i211/lab8) $ cd ..
jpr@sulu (i211) $ tar czv lab8 > lab8.tar.gz
socialnet.pl
jpr@sulu (i211) $

You should then download this lab8.tar.gz file and upload to the Lab 8 assignment on Oncourse. Make sure you press "submit" and "finish" enough times to actually upload your file. We will take off points for incorrect submissions, even if you really finished the lab on time.

Okay, that's it! Have a good weekend.
Image from http://www.research.ibm.com/thinkresearch/images/20050706_hpf_think.jpg
Thanks to Jacob Ratkiewicz for lab content, Sid Stamm for CSS stylesheets, and Rob Signorelli for original syntax-highlighting JavaScript.