Ruby Topic Maps Tutorial (2007-10-10)

Getting started with

Ruby Topic Maps
Benjamin Bock

Third International Conference on Topic Maps Research and Applications
Tutorials@TMRA Leipzig, 2007-10-10

Why Ruby?

interpreted, object-oriented
programming
features procedural and
functional paradigm
everything is an object

dynamic and (but) strong typed
2

What about Rails?

Model-View-Controller

Convention over Configuration

Optimized for programmer
happiness and productivity

3

… and Ruby Topic Maps?

Web 2.0 is about integration

Ruby and Ruby on Rails are big
players there

Topic Maps nonexisting in the
Ruby world
4

Schedule

Introduction
Software distribution
Programming Ruby
Ruby Topic Maps
Rails Basics
Using RTM in Rails

5

Command line tool
irb: Interactive RuBy

Windows:
Click start -> run -> “cmd” -> “irb”
Mac OS X:
Start the Terminal -> type “irb”
Linux:
Open a shell -> type “irb”

That’s what you get:
irb(main):001:0>
6

Calculator

irb(main):001:0> 1+2

irb(main):002:0> 3*4

irb(main):003:0> 5**3

irb(main):004:0> Math.sqrt(81)

7

Simple Types

# comment until end of line
quot;Stringquot;
1 # number
1.0 # floating point number
1_000_000_000_000 # BigNum
:symbol # these are important!
true, false, self, nil
8

Even More Types

[1,2,3] # Array
{ :key => quot;valuequot; } # Hash
/regular expression/
(1..10) # exclusive Range
(1...10) # inclusive Rage
# Files are also basic types,
# but what does that mean?
9

Numbers

123 1_234 123.45 1.2e-3
0xffff (hex) 0b01011 (binary)
0377 (octal)
?a # ASCII character
?C-a # Control-a
?M-a # Meta-a
?M-C-a # Meta-Control-a
10

Strings
'no interpolation'
quot;#{interpolation}, and backslashesnquot;
%q(no interpolation)
%Q(interpolation and backslashes)
%(interpolation and backslashes)
`echo command interpretation with
interpolation and backslashes`
%x(echo command interpretation with
interpolation and backslashes)

`ls` # returns output of system command ls
11

Methods
def hello
puts quot;helloquot;
end

def salute(who)
puts quot;Hello #{who}quot;
end

def salute(who=quot;worldquot;)
puts quot;Hello #{who.capitalize}quot;
end
12

Method Invocation
method
obj.method
Class::method

# keyword parametres: one argument for def method(hash_arg):
method(key1 => val1, key2 => val2)

becomes: method(arg1, arg2, arg3):
method(arg1, *[arg2, arg3])

#as ugly as you want it to be:
method(arg1, key1 => val1, key2 => val2, *splat_arg) #{ block }

# A bit more formal:
invocation := [receiver ('::' | '.')] name [ parameters ] [ block ]
parameters := ( [param]* [, hashlist] [*array] [&aProc] )
block := { blockbody } | do blockbody end

13

Everything is an Object

nil.class
true.object_id
2.75.ceil
5.times do # this a preview,
details later
puts quot;I like Ruby!quot;
end
14

Everybody is valuable
# ... and everything has a value

# often no quot;returnquot; statements needed
def value
5
end
x = value # x = 5
y = if 1 != 2 # even if has a value
quot;rightquot;
else
quot;wrongquot;
end
# y == quot;rightquot;
15

But what if ...
if condition [then]
# true block
elsif other_condition # not elseif!
# second true block
else
# last chance
end

# also:
z = condition ? true_value : false_value
16

Can you tell me the
truth?
# Yes, it's 42

if 0 then
quot;this is the casequot;
else
quot;but this will not happenquot;
end

# Only false and nil are not true!
# That's handy for == nil checks.
17

the case is as follows
case my_var
when quot;hiquot;, quot;helloquot;, quot;halloquot;, quot;salutquot;
puts quot;it was an greetingquot;
when String
puts quot;it was a string...quot;
when (1..100)
puts quot;A number between 0 and 100quot;
when Numeric
puts quot;A number not in the range abovequot;
else
puts quot;What did you give me here?quot;
end
end
18

Back to the Question
# there are other conditionals

return false if you_dont_like_to_answer

unless you_are_already_asleep
i_will_go_on
end

# this is not a loop!

19

Iteration Iteration Iteration Iteration

5.times { |x| puts x }
[quot;alicequot;, quot;bobquot;].each do |name|
puts quot;Hello #{name}quot;
end
list = [6,7,2,82,12]
for x in list do
puts x
end
20

go_on until audience.asleep?

loop do
body
end

{while,until} bool-expr [do]
body
end

begin
body
end {while,until} bool-expr
# we have: break, next,redo, retry

21

Blocks (a.k.a. Closures)
search_engines =
%w[Google Yahoo MSN].map do |engine|
quot;http://www.quot; + engine.downcase +
quot;.comquot;
end

%w[abcde fghi jkl mn op q].sort_by { |
w|
w.size
}
22

Object Oriented Constructs

$global_variable
module SomeThingLikePackageInJava
class SameLikeJava < SuperClass
@instance_variable
@@class_variable
def initialize()
puts quot;I am the constructorquot;
end
def method(param, optional_param=quot;defaultquot;)
quot;This String is returned, even without return
statementquot;
end
end
end
SomeModule::CONSTANT
23

Meaningful Method Names
# usage: some_object.valid?class Person
class Person
def name; @name; end
def name=(new_name)
@name = new_name
end
def valid?
return true unless name && name.empty?
false
end
end
class Person # almost the same
attr_accessor :name
def valid?; name && ! name.empty?; end
end
p = Person.new
person.valid?
person.name = quot;Benjaminquot;
person.valid?
24

Only one aunt may die
# single inheritance only

# alternative model: mixins

class MyArray
include Enumerable
def each
# your iterator here
end
end
# Enumerable provides:
all? any? collect detect each_with_index entries find
find_all grep group_by include? index_by inject map max
member? min partition reject select sort sort_by sum to_a
to_set zip
25

Ruby is flexible

class Numeric
def plus(x)
self.+(x)
end
end

y = 5.plus 6
# y is now equal to 11
26

Redefining Methods
warn(quot;Don't try this at home or at allquot;)

class Fixnum
def +( other )
self - other
end
end

5+3
# => 2
27

Introspection
# Tell me what you are
5.class
quot;qwertyquot;.class

# Tell me what you do
[1,2,3].methods

# this is how I got the list above
Enumerable.instance_methods.sort.join(quot; quot;)

# Would you? Please...
some_variable.respond_to? :each

28

Missing Methods
# id is the name of the method called, the * syntax
collects
# all the arguments in an array named 'arguments'
def method_missing( id, *arguments )
puts quot;Method #{id} was called, but not found. It has
quot;+
quot;these arguments: #{arguments.join(quot;, quot;)}quot;
end

__ :a, :b, 10
# => Method __ was called, but not found. It has these
# arguments: a, b, 10

29

eval is evil...
class Klass
def initialize
@secret = 99
end
end
k = Klass.new
k.instance_eval { @secret } # => 99

# generally:
eval(quot;some arbitrary ruby codequot;)
30

...but may be really helpful
eval(string [, binding [, filename [,lineno]]]) => obj
mod.class_eval(string [, filename [, lineno]]) => obj

# there are many blocks like this in the RTM source
code
module_eval(<<-EOS,
quot;(__PSEUDO_FILENAME_FOR_TRACES__)quot;, 1)
def #{method_name_variable}
some custom method using #{more} #{variables}
end
EOS

31

Something (not so) exceptional

begin
# some code
# may raise an exception
rescue ExceptionType => ex
# exception handler
else
# no exception was raised
ensure
# this stuff is done for sure
end

raise Exception, quot;Messagequot;

32

Things we do not cover here

alias
here docs
regex details
access restriction
predefined variables: $!, $@, $: ...
backslash constructions: n t
and some other
stuff we do
not need
today
33

Sources
http://www.ruby-lang.org/en/about/

http://www.ruby-lang.org/en/documentation/ruby-from-
other-languages/

http://www.zenspider.com/Languages/Ruby/QuickRef.html

http://www.ruby-doc.org/core/

34

Break
require 'timeout'
begin
status = Timeout::timeout(30.minutes) do
ingestion = Thread.start do
loop { get_coffee; drink; sleep(30); }
end
chat = Thread.start do
loop { sleep(15); talk; listen; smile; }
end
end
rescue Timeout::Error
puts quot;Let's get back to workquot;
end
35

Demo session

# Seeing is believing… :-)

36

# loading the Ruby Topic Maps library
# in a script or in environment.rb
require 'rtm'

# a new module called RTM will be
# loaded into the default namespace

# To get direct access to constants like
# PSI, a hash of TMDM subject indicators
# use
include RTM

37

# Connecting to a back end
# Memory
RTM.connect
# File database, default is tmdm.sqlite3
RTM.connect_sqlite3
# Custom database file
RTM.connect_sqlite3(quot;filename.dbquot;)
# Standard MySQL database
RTM.connect_mysql(quot;database_namequot;,
quot;user_namequot;, quot;passwordquot;, quot;hostquot;)
38

# At first time use, we have to generate
all the tables in the database
RTM.generate_database

# for now, we use memory database
RTM.connect
# or
RTM.connect_memory

# enable SQL statement logging
RTM.log
# defaults to STDOUT, configurable as Logger
39

Ruby on Rails

# Get on the Train!
# Can I see your ticket, please?

40

Hands-on

# Now, it’s your turn… :-P
(again)

41

Fin
begin
puts quot;Questions?quot;
x = gets
puts response_to(x)
end until x =~ /(no|exit|quit)/i

puts quot;Thank you very much?quot;
42

Ruby Topic Maps Tutorial (2007-10-10)

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