Service Description Language Framework

This is a framework for the easy description of business aspects of internet services using self defined vocabularies.

Its main features are:

  • Comprehensive textual domain-specific language
  • DSL implemented as Ruby code, allowing flexible use cases (e.g. extracting data from websites)
  • Export of services and vocabulary to XML/XSD and RDF
  • Internationalization of vocabulary descriptions

Upcoming features include:

  • Definition of service property comparison
  • Input alignment (e.g. matching country to jurisdiction)
  • Property type enforcement / type conversion
  • Feature model based service variant management
  • Modelling of dynamic pricing

The main design constraints for the framework are:

  • A text editor should suffice to create service descriptions and vocabulary
  • Compared to other general SDLs, e.g. USDL, Linked-USDL, and OWL-S syntactic and semantic noise should be reduced
  • Concrete serialization technologies should be abstracted, such as XML/XSD, RDF/OWL and EMF/Ecore
  • There is no common answer to "What is a service?". Therefore the structure of service descriptions should be provided by concrete use cases, and not the framework itself
  • The functionality of the framework should be demonstrated on existing services
  • Using a programming language as textual format should allow both static and dynamic information to be available in the same file

The SDL Framework is the basis of the TRESOR Broker, and will be supporting the "Open Service Compendium", an envisioned crowdsourced repository for service descriptions, their comparison and brokering.

General Overview

The SDL Framework allows the definition of vocabulary and service descriptions. The vocabulary defines "What can generally be known about any service" (a so called meta-model). Service descriptions refer to defined vocabulary and define "What is known about a specific service".

For example, a vocabulary defines that "services can be accessed using a browser" and that "there are different browsers in existence", while the service description of a concrete service, e.g. Salesforce Sales Cloud, defines that it can be accessed using Internet Explorer 7+, recent versions of Firefox and Chrome and Safari 5+ on mac. (see examples/service_definitions/salesforce_sales_cloud.service.rb for more examples)

The vocabulary

A vocabulary defines fact classes, SDL types, properties, and SDL type instances.

Any fact class, property value and type instance can be annotated with arbitrary data to capture "fine-print" of descriptions.

Fact classes

A fact class is a class of possible statements about a service. Some examples are:

Class name Statement
BrowserInterface It can be accessed using a browser
CloudServiceModel It can be categorized by a cloud service model
CommunicationProtection It is protected by a communication protection
EstablishingYear It has a defined year of establishment

SDL Types and type instances

An SDL type is used for structuring fact information.

Within a vocabulary, SDL types can be instantiated. These SDL type instances can be easily referred to from fact instances by their name. This allows different service descriptions to refer to the same instances.

The following table shows some examples of types, their purpose, and predefined instances:

Type name Used with Description Instances
Browser BrowserInterface A web browser Firefox, Chome, Opera
CloudServiceModel CloudServiceModel A cloud service model SaaS, PaaS, IaaS
CommunicationProtection CommunicationProtection A way to protect service communication VPN, HTTPS

Fact and Type Properties

Properties give more information about facts and types. Every property has a name, type, and can be multi valued (a list).

Some example properties are:

Defined on Name Type Multi-valued Definition
BrowserInterface (Fact) compatible_browsers CompatibleBrowser Yes A list of compatible browsers
CompatibleBrowser (Type) browser Browser No A browser
Browser (Type) url URL No The URL of a Browser
CloudServiceModel (Fact) cloud_service_model CloudServiceModel No The cloud service model
CommunicationProtection (Fact) communication_protection CommunicationProtection No The communication protection of the service
EstablishingYear (Fact) year Integer No The year a service was established

Types can be either types wrapping Ruby classes, e.g. dates, durations, strings, numbers and URLs, and also other SDL types.

Service Descriptions

A service description uses fact classes, types, and type instances to describe services.

Vocabulary Syntax

This chapter defines the syntax of vocabularies.

Fact class and type definition

The fact class and type definition are very similar.

This is how fact classes are defined:

fact <symbolic name> do

<Fact properties and subfacts>

end

And this is how types are defined:

type <symbolic name> do

<Type properties and subtypes>

end

Every fact class and type definition is identified by its symbolic name, for which the SDL framework creates a Ruby class:

Symbolic name Ruby class constant name
:name Name
:payment_option PaymentOption
:compatible_browser CompatibleBrowser
:browser Browser

The definition block includes properties and subclasses of fact classes and types respectively.

Property definition

Fact and type properties are defined according to the following pattern:

<type> <name>

<type> can refer either to a wrapped type or another SDL type.

Wrapped types wrap Ruby classes. The following are available (see lib/sdl/types):

Wrapped Ruby Type Referenced as
String string, str
Integer number, integer, ├Čnt
Time datetime
ActiveSupport::Duration duration
URI uri, url

SDL types are referred by their name, e.g. payment_option references PaymentOption.

Properties can be multi valued, denoted by a list_of_ prefix, e.g. list_of_strings or list_of_browsers.

<name> can be omitted, if it is the same as the name of the type. The following type definitions are equal

url

equals

url :url

Type instances definition

Predefined type instances are created using the following pattern:

<type reference> <symbolic name> do

<property definition>

end

If a browser type is defined as such:

type :browser do
  url
end

Instantiating browsers can be done like this:

browser :firefox do
  url 'http://www.mozilla.org/firefox/'
end

browser :chrome do
  url 'https://www.google.com/chrome'
end

browser :internet_explorer do
  url 'http://windows.microsoft.com/en-US/internet-explorer/download-ie'
end

Subtype and subfact definition

As types and facts are Ruby classes, they can be inherited.

This is how subclasses of fact classes are defined:

fact <symbolic name> do

subfact <symbolic name> do

<Subfact properties and further subfacts>

end

end

It is very similar to subclasses of type classes:

type <symbolic name> do

subtype <symbolic name> do

<Subtype properties and further subtypes>

end

end

Service definition syntax

The service definition contains any number of lines following the pattern:

<fact class reference> <property setting instructions>

There are different ways how to reference facts and set property values, shown in the following subsections.

Fact class reference

Fact classes can be referred by three different mechanisms: either has_<fact name>, or <fact name>, or is_<past perfective of fact name as verb>. This allows choosing a term which has the highest readability for a certain fact class.

The following table contains some examples:

Fact class has_<fact name> <fact name> is_<past perfective of fact name as verb>
Name has_name name is_named
Bill has_bill bill is_billed
Feature has_feature feature is_featured

Property setting instructions

Setting the values of fact and type properties can be done in two ways:

Short form

If a fact or type has only some properties, setting properties can be done by specifying their values in the order they appear in the vocabulary:

<fact or type reference> <first value>, <second value>, <n-th value>

The following example (taken from examples/service_definitions/google_drive_for_business.service.rb) illustrates this mechanism:

name 'Google Drive for Business'

has_add_on_repository 'https://www.google.com/enterprise/marketplace/home', 1000

If properties should be set in a different order, the property names can be specified as:

<fact or type reference> <name> : <value>, <name> : <value>, ...

An example would be:

has_documentation url: 'http://www.salesforce.com/sales-cloud/overview/'

The default Ruby syntax applies for creating lists: [ <item 1> , <item 2> , <item n> ]

It should be obvious that the order of values has to change if the order of properties changes.

Block form

If a fact or type has many properties, setting those can be done as a block:

<fact or type reference> do

<name> <value>

end

The following example (see examples/service_definitions/salesforce_sales_cloud.service.rb) illustrates this mechanism:

has_add_on_repository do
  url 'https://appexchange.salesforce.com/'
  number_of_add_ons 2000
end

Multi-valued properties are created by specifying the name more than once, for example:

has_browser_interface do
  compatible_browser ...
  compatible_browser ...
  compatible_browser ...
  compatible_browser ...
end

Combining both methods

Both methods can be combined:

<fact or type reference> <property setting instructions> do

<name> <value>

end

So the example of the previous subsection can be rewritten as:

has_add_on_repository 'https://appexchange.salesforce.com/' do
  number_of_add_ons 2000
end

Referencing type instances

Type instances can be referred to by using name, as for example:

has_cloud_service_model saas

Due to the inner workings of the framework, if there are different instances with the same name, then the name has to be prepended by a colon (:), for example:

has_cloud_service_model :saas

Annotating data

Annotations can be used to capture the "fine-print" of service descriptions.

By adding annotation: annotation any property value definition and fact instance can be annotated, for example:

has_cloud_service_model :saas, annotation: "Unless you are Deutsche Bank"

has_add_on_repository 'https://appexchange.salesforce.com/' do
  number_of_add_ons 2000, annotation: "... and rising every minute"
end

Using Ruby code for crazy stuff

As all service descriptions and vocabulary are Ruby code, any functionality can be integrated into the descriptions.

The following code example uses the helper function fetch_from_url which uses Nokogiri to fetch a url and filter it according to a CSS selector to retrieve feature descriptions:

features = fetch_from_url 'http://www.salesforce.com/sales-cloud/overview/', '.slide h3 + p'

has_feature 'Mobile', features[0]
has_feature 'Contact Management', features[1]
has_feature 'Opportunity Management', features[2]
has_feature 'Chatter', features[3]
has_feature 'Email Integration', features[4]

Interfacing with the framework

As the framework is to be used within other applications, there is no mening to "running" it.

Nevertheless, there is a GEM binary, process_service_descriptions provided, which does the following:

  • Load translations from the translations directory
  • Load all vocabulary definitions from the vocabulary directory
  • Use this vocabulary to process all service descriptions from a services directory
  • Output XML/XSD, RDF and Markdown to the output directory

This binary can be used within the examples subdirectory of this GEM.

Examples

To run all examples, execute the GEM binary process_service_descriptions within the examples subdirectory of this GEM.

Google Drive for Business

Included from examples/service_definitions/google_drive_for_business.service.rb

Salesforce Sales cloud

Included from examples/service_definitions/salesforce_sales_cloud.service.rb

The most basic example

This vocabulary specifies that services can have an availability, expressed as an integer:

fact :availability do
    integer :availability
end

This defines a Fact class Availability, with an integer property availability which can be instantiated within service descriptions as:

has_availability 100

or just

availability 100

If service would be a service description object, this would output 100

puts service.availability

The definition of color

The following type class definition is used to specify that the type :color is defined by a hexadecimal value, stored in a string.

type :color do
    string :hex_value
end

It is now possible to define instances of this type and assign them symbolic names, such as red, green or blue:

color :red do
    hex_value '#F00'
end

color :green do
    hex_value '#0F0'
end

color :blue do
    hex_value '#00F'
end

After definition of types, a service fact class can be defined, referring to this type.

fact :color do
    color :color
end

Now, differently colored services can be described, e.g.:

red_service.service.rb:
    has_color :blue

green_service.service.rb:
    has_color :green

blue_service.service.rb:
    has_color :blue

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request