This is a quick blog post on how to install and use the Relational Algebra Interpreter on a Windows machine.
#1 What is the Relational Algebra Interpreter?
You only need the Relational Algebra Interpreter if you have a database that you set up through SQLite or MySQL or other database software (not Microsoft Access) and you want a shortcut to writing the SQL commands like SELECT and PROJECT.
The Relational Algebra Interpreter was written Jun Yang, now of Duke Uni. It is used by many universities, including Stanford, to teach database programming.
#2 Install the Relational Algebra Interpreter?
This notes describe my installation. I am not an expert and I am jotting down what I did mainly so that I can do it again another day. If they help you, good; if not, sorry.
#2.1 Do you have Java installed on your machine. I am using Windows 7 on a relatively new machine and I have a Java JRE (runtime environment) installed but not a JDK (development kit). I didn’t want to rush a notoriously convoluted Java install and make a mess of a new machine, so I fired up my old Windows XP where there is a JDK already installed.
#2.2 Decide where to put your RA interpreter.
The Interpreter comes with everything you need to run on SQLITE databases ( I am not sure on what else) and as I am only using the RA interpreter for a few weeks, I didn’t want to change my PATH statement – so I made a working folder, e.g. C:/A_RA_demo.
I went to Dr Yang’s page and downloaded the RA Interpreter and unzipped it. I also transferred over from my other machine the test SQLITE3 database that I made earlier (see another post).
#3 Use the Relational Algebra Interpreter
#3.1 The RA Interpreter file runs from your command prompt (Go to Start; type cmd in the box and hit enter; change directory to work in your working directory, e.g., cd c:/A_RA-demo.
#3.2 The RA Interpreter comes with a sample.db and a sample.properties file. So to prove everything works, type into your command line, “java –jar ra.jar” and observe the changes on your screen.
#3.3 See what is in the sample.db by typing at the ra> prompt “list;”.
#3.4 Pick any of the “relations” (tables in plain English) and type at the ra> prompt “relationname;”.
#3.5 Type at the ra> prompt “quit;”
#4 Use the Relational Algebra with your own database
#4.1 To use the Relational Algebra with your own database, you must make a corresponding .properties file.
#4.2 Copy the sample.properties file and save it as yourdatabasename.properties.
#4.3 Find the right command line to edit. Most of the file is commentary.
#4.4 I was using a database made in SQLITE3 so I picked the SQLITE command. You don’t have to add a 3. You must change the sample.db to the yourdatabasename.extension. I got held up here for a while because my database was a just a file without an extension. When I typed in the database-name-only, it worked.
#4.5 Go back to the command line and make sure you are working in the working directory. If not, look at step #2.2
#4.6 On the command line, type “java –jar ra.jar yourdatabasename.properties”
#4.7 Confirm you have read your database by typing at the >ra prompt “list;”
#4.8 All working? So quit for now by typing at the >ra prompt “quit;”
#5 Use the Relational Algebra Interpreter with query commands in a file.
#5.1 Put the relational algebra interpreter commands in a text file and save in the working directory (e.g., query1.txt). [You could test “list;” for now.]
#5.2 Go back to the command prompt and confirm you are in your working directory. Type “java –jar ra.jar yourdatabasename.properties –i query1.txt”
#5.3 You will get an answer, or more likely an error message. Debug your query, resave query1.txt and rerun the java line. Conveniently, recall the java line with the up key and enter.
Done! Now all you have to do is learn the Relational Algebra syntax which you can also find on Professor Yang’s site. It is a little mind blowing and I found tracking all the brackets quite hard but you get the hang of it with practice.
Make sure you start with a little database so you can check your queries by hand. And search the Stanford website for class notes to help you on your way.
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