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Short Description Relation Algebra Interpreter
Full Description Relation Algebra Interpreter, Copyright (c) 2016
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--------------------------------------------------------------[ Introduction ]--

The ``Relation Algebra Interpreter'' (or short RA Interpreter) is a program
which can read CSV tables and perform some basic relation algebra on it, that
is to say: Project, Join and Select operations.

This program was written for learning purposes. If you find it useful for
anything else, keep in mind, that it was probably not designed to do what you

---------------------------------------------------------------[ Compilation ]--

If you are on a Linux system with the GNU Ada Compiler GNAT installed, it should
be enough to type make to build this program. If you want to use Docker, you
may either build this image with docker build . or run it directly with

docker run -it --rm masysma/uni-dke-u03-11-ra-interpreter

Otherwise, you will need to compile the program with any Ada 2012 compiler.
The main file is ra_interpreter.adb.

---------------------------------------------------------------------[ Usage ]--

The program runs interactively on the console and takes commands as input
and prints resulting tables directly to the console.

Format your files as comma separated value, for example like test/t1.csv


The first row is considered the schema of this relation which you can
interactively load as follows:

RA> read(t1, test/t1.csv)

You will not get an answer, because you just load the relation into memory
under the name t1 (first parameter to read).

In order to print a table, select all of its rows:

RA> SEL[1](t1)
  File                Lines  
+++++++++++++++++++++++++++++             24     
  ra_interpreter.adb  26             32            37     

It pretty-printed the relation.

Now, let's add a condition to the select statement:

RA> SEL[(File = "")](t1)
  File     Lines  
++++++++++++++++++  32     

Note the parentheses around the condition, we wrote SEL[(...)]. If you consult
what help has to say about this:

RA> help
Bool:  (v = v)    Compares values.

It says, that you have to put a comparison in parentheses This simplifies
parsing but is a bit more to write. Also, comparison only works for values.
You cannot compare Booleans with this program.

Finally, let's have a look at an example for Natural Joining. Load the relation
from test/t2.csv as t2 and perform a join on the two tables:

RA> load(t2, test/t2.csv)
RA> JOIN(t1,t2)
  File                Lines  Size/Bytes  
+++++++++++++++++++++++++++++++++++++++++             24     858         
  ra_interpreter.adb  26     1038              32     1126             37     1400        

... It works as expected joining the two relations on the common field File.

Explore the other options by viewing help. Most of them work as expected.

--------------------------------------------------------------------[ Issues ]--

As this was created for learning purposes, it's features are only rudimentary.
Especially, you can not

  • Recall commands via a history
  • Use another syntax than given there, spaces are sometimes relevant!
  • Do a lot of boolean operations
  • Use fields longer than 256 characters :(

Programming Language
This was written in Ada as a means of getting to know that language.
Thus, there are probably a lot of beginner's mistakes in there...

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