Object-oriented design is well known since 20 years. Domain specific languages and domain driven design have become popular with dynamic languages such as Ruby or Python. If your domain consists mainly of objects, for example a subystem to grant badges or achievements (like the badges on Stackoverflow), then one could use both, object-oriented design and domain driven design, since a badge is certainly an object. For example for Ruby, there are two gems to implement this functionality, Badgeable and Paths of Glory. Badgeable uses a DSL, Paths of Glory is based on an object-oriented design. In which cases is it better to use modeling by object-oriented analysis & design, and for what cases is it preferable to use modeling by a domain specific language (i.e. domain driven design)?
OOD and DDD are not interchangable things.
A DDD will very often involve using OOD.
From the Wikipedia page:
Domain-driven design is not a technology or a methodology. DDD
provides a structure of practices and terminology for making design
decisions that focus and accelerate software projects dealing with
complicated domains.
In particular, read the Relationship to other ideas part.
Related
Currently i am trying to figure out, then to use OWL and then to use UML to describe a domain of interest in a Software Engineering process.
I read this paper by Atkinson, which gives a very good overview about the difference and the equalities of OWL and UML on a semantic and a syntactic level.
However it does not provide a clear indication in which use-cases it might be better to use OWL instead of - for example - an UML class diagramm.
It might be the underlaying development process, which decides the modelling language to take (e.g. model-driven = go for UML, ontology-driven = go for OWL) but for myself it is this difference still not clear?
In both language I can build up a terminology, which I - as an ontology engineer - can reuse in order to infer new knowledge from it. As an Software Engineer I use this terminology for the construction of a (single) system.
So is the difference between OWL and UML just the field of study? Or could I use OWL in order to describe the construction of my (single) software system?
Moreover, this raises the question if the decision of which kind of modelling language to choose is only driven by the goal, which I try to accomplish?
A synthetic answer
UML is a (graphical) language for modeling
OWL is a language used for knowledge representation (KR) in a semantic perspective
In the first place, OWL purpose is not modeling. Using a KR technique is an option in the field of software engineering. It should be distinct from any software engineering process. Both languages have different purposes.
Of course, you could [use] OWL in order to describe the construction of [a software system]. But the interest of such a move would mainly be in automated reasoning about your software construction process and would not be very helpful in the context of a single project. This would only be effective if done for all your projects in order to have a consequent knowledge base (KB).
A detailed explanation
According to the W3C wiki section about OWL:
The W3C Web Ontology Language (OWL) is a Semantic Web language designed to represent rich and complex knowledge about things, groups of things, and relations between things. OWL is a computational logic-based language such that knowledge expressed in OWL can be exploited by computer programs, e.g., to verify the consistency of that knowledge or to make implicit knowledge explicit
There should be some debate about what is a modeling language. For example, the Wikipedia article on the topic considers a broad sense which could also cover OWL. I consider here with the modeling term only the software engineering activity (which is the one you focus on in your question).
You might need modeling in order to define ontologies, just like you would need for the development of a software project. But this OWL modeling would not consider the software engineering elements but rather the domain data of your project. In other words, using UML in a software construction process aims to setup software elements. With OWL, you would not focus on these elements, unless you are trying automated reasoning about software construction.
Beside this, a relationship exists between UML and OWL. A note by Walter W. Change in the frame of the W3C discusses the question. I would summarize the question considering two distinct relations.
Using UML to represent OWL knowledge
An OMG specification called ODM (for Ontology Definition Metamodel) provides a metamodel for defining ontologies. In the frame of this specification, the use of an UML profile is introduced as a way to bridge a gap between both languages. In the ODM 1.1 specification, section 8.4.2:
The goal of a UML profile from the ODM perspective is to provide a bridge between the UML and knowledge representation communities on a well-grounded, semantic basis, with a broader goal of relating software and logical
approaches to representing information.
The UML profile use is introduced in an article. You might find such a profile in the ODM 1.0 specification resources, as a non-normative document. According to what is here considered, this UML profile might be a tool for modeling ontologies.
Using OWL/Semantic Web technologies to represent UML
RDF is the basis format used to write OWL ontologies.
An early (2000) academic work provides a semantic RDF document modeling the UML elements (based on the OMG specification). This work preceded the draft works on the OWL W3C recommendation (2002).
Actually OWL is available as profile in UML. See OMG specfication. So you can use UML with OWL profile in "one soup".
Let's start with the definitions.
Unified Modeling Language (UML) is a general-purpose, developmental,
modeling language in the field of software engineering, that is
intended to provide a standard way to visualize the design of a
system. (Wikipedia)
UML has many diagrams, but none of the classics is designed for ontology modelling. Therefore, researchers have created OWL with this purpose.
The W3C Web Ontology Language (OWL) is a Semantic Web language
designed to represent rich and complex knowledge about things, groups
of things, and relations between things. (W3C)
Such as said by Thomas Kilian in the other answer:
OWL is available as profile in UML. See OMG specfication. So you can
use UML with OWL profile in "one soup".
Therefore, OWL can be part of the set of UML diagrams used in a Software Engineering Process. The main benefit of OWL over classic UML diagrams is when you have to design a system using ontologies. The purpose of class diagrams is to represent classes, not ontologies. If your system does not rely on ontology, stick with the classic UML diagrams; you do not need OWL. If your system uses ontology and you need to represent it on a diagram, use OWL.
OWL is used to describe a domain and to be able to specifically, using semantics, specify knowledge of a domain as well as describe its specificities. Take for example the Friend of a Friend ontology. Using it you can describe how people relate to each other.
You might say that you can do the same thing using UML and you are correct. You can specify properties, relations, and so on, using OWL as well as UML. However, what you can't do with UML is infer domain knowledge. OWL, being a Semantic Web language, models a domain with either an Open or Closed World assumption. Basically you assume knowledge based on what is described in the domain. Then you can use specific instructions to infer knowledge using Rules or just be looking at predicates and statements you have created. Furthermore, you can use specific query languages such as SPARQL to query your ontology as much in the same way you would use SQL to query a database.
TL;DR: Using UML you specify how you would translate a specific domain into software, using OWL you specify knowledge about the domain as it is much richer than UML.
To amend the references of UML and OWL comparison there is a PhD thesis (in German) from Jesper Zedlitz Konzeptuelle Modellierung mit UML und OWL – Untersuchung der Gemeinsamkeiten und Unterschiede mit Hilfe von Modelltransformationen
(Conceptual Modeling with UML and OWL - Exploring the Similarities and Differences Using Model Transformations)
In this thesis studies if and in which extend it is possible to tranform between both modelling languages. In the conclusion (p. 222) it is stated that OWL has possibilities to do more complex modelling and therefore it is not always possible to transform from OWL to UML.
Actually from my work on ontologies in the previous time I see using ontology tools like Protege is very helpful and rich in describing relations between entities and using Tools like OLGA can help you in mapping this ontology to many object oriented language.
Yes, we haven't the capabilities of using graphical representations to design our models like UML but it provides a wide range of options to describe you model.
The importance and benefits of mapping the domain ontology to the UML model are in integrating the benefits and quality that these two modeling techniques provide. That is, if there are already domain ontologies with a certain level of authority, these knowledge bases can help in the creation of UML class diagrams, such as the axiomatic guarantees provided by the description logic that builds it, besides enabling UML power of inferences Provided by this formalism, with the transformation is intended to show the evidence that reuse of ontology can help to reduce ambiguity in class diagrams.
James Neighbors mentioned DSLs as an approach for software reuse but without explaining why.He just say that DSLs can be a better approach than a library of reusable components. I could not understand the relationship and what benefits can we come up with using DSLs in software reuse ?
Also in When and How to develop DSLs paper by Mernik , he mentioned that DSLs can serve as an input language to application generators, and application generators is one approach of reusing software discussed by Krueger.
Could anybody tell me the relationships or just how would a DSL be an effective approach towards software reuse ? Thanks a lot for your help
James made it very clear why DSLs are a good approach for software reuse (he and I were at UC Irvine together):
They capture the concepts of interest in the problem domain
They use a notation familiar to community that works in that domain
They define the rules of composition of specification/solution components to produce an answer, so that a DSL fragment can be checked for sanity as it is provided
His Draco system implemented all these concepts, accepting DSL descriptions, followed by a DSL instance, which Draco then compiled to low level code by applying implementation knowledge fragments ("refinement rules") to map from a high-level DSL into lower level DSLs/optimizing in the lower level DSL, and then repeating until you finally reach a DSL at low-enough level abstraction to give to a conventional compiler (e.g, to LISP or C or Ada or COBOL or ...).
This is his refine-and-optimize paradigm, that allows a set of DSLs to refine through layers of hierarchy to low level code. Thus, you get composability of layered domains and you can work at a very high level of abstraction.
So you capture problem specification and implementation knowledge, and apply it to get code. Reuse of abstractions, of specifications, of implementation, wow, ... not just reuse of "code" which is where lots of folks still seem stuck, as they were in the early 80s. Code is really hard to reuse.
This is really a very nice paradigm compared to "subroutines-as-components" (the fancy term for this currently is "inner DSL", which misses the domain notation, specification checking, implementation, and compositionality elements).
I think you really ought to read his PhD thesis (accessible here along with a lot of his other papers) carefully. It is a lot more approachable than might expect. It isn't full of arcane math; it is full of concepts and demonstrations of how to engineer his kinds of DSLs.
Is it appropriate to think of UML as a DSL?
I know that everybody thinks of UML as a way to draw pictures, but underlying the "view" of UML diagrams there is a model...and the "L" in UML stands for Language.
Another question - is SysML a DSL?
UML is a DSL.
A "domain specific language" lets one specify a problem or a solution in a narrow area of application; banking, telephony circuit design, .... One way to distinguish a DSL is that it cannot do general purpose computation (although there are some DSLs that can). Java, C#, Python and COBOL fail this test. (Some would say COBOL is domain-specific for "business" but its only serious concession to that is a decimal data type, and C# has that too.) ColdFusion fails this test; nonstandard syntax does not a DSL make, but IIRC ColdFusion has some support for generating HTML. Fortran fails this test, but its array(-section) sublanguage is only good for arrays and not general purpose computation. Verilog is very domain specific: it is designed to let you write down digital circuits.
UML focuses on specifying different aspects of how software is structured. [You'll note it can't do general purpose computation; one hallmark]. (It actually has 9 or more different aspects it addresses: classes, statecharts, deployment, ... I'll stick to the class aspect for this discussion). The class diagram aspect lets one describe how data is organized, and operations on that data. You can argue this about software so it can't be "domain-specific". What, building software isn't a problem domain?
SYSML is focused on expressing how systems are joined, so it fits this category too.
A more useful question to ask IMHO is, "If I think of UML as a DSL, what do I gain?" Here I don't think you get a lot. The concept of DSL is useful when you arguing for one you don't have (designed or possess) with the point being better expressiveness for a common problem, and might be useful for arguing "you don't want implement your system entirely in it because it isn't Turing capable". It is also useful if you want to explain that your language is going to have a lot of funny notations, precisely because they serve special purposes. People already know this about UML, so... nothing learned.
While I'm a big fan of DSLs, I'm also a big fan of GPLs (general purpose languages). I think in big systems you should necessarily find a "lot" of both: the DSLs to express what they can succinctly (cuts engineering and maintenance costs), and the GPLs to provide arbitrary computation and glue between the system parts. For me what counts in a language is:
what's the class of problem it claims to address and how well does it do it?
what's the syntax (and is it relatively standard for the problem domain)?
what are the precise semantics (this is where you learn the most)?
how good is the tool support?
how well does the DSL integrate into other parts of a big system?
how big and supportive is the community?
UML has (after 15 years) arrived at pretty good answers to these questions.
Homegrown DSLs often don't do so well, partly due to poor design, but often due to the fact that tool support is difficult to get. My company provides machinery to give DSL builders excellent support to improve this situation.
UML is NOT a DSL because UML can be used to model any vertical domain (insurance software, embedded systems,...)
UML is a (horizontal) DSL because UML is a specialized language to model software systems.
So UML is and is not a DSL depending on how you look at it. You could apply the same reasoning to many other languages like html or SQL. They are general because they can be used to represent/manipulate any kind of data but they are specific because they are focused on one task
Short answer - NO - to both questions.
Think of UML as a tool that lets you describe software architectures, software interactions and so on ... describe them in a general way, language agnostic.
DSLs are specialised syntaxes meant to make it easier to describe some specific set of problems
I think the answer to your first question depends on how to define "General" in the term "General Purpose Language". Wikipedia says it is not a DSL:
The opposite is:
a general-purpose programming language, such as C, Java or Python,
or a general-purpose modeling language such as the Unified Modeling Language (UML).
I am a MDA enthusiast so I think I can provide you a very detailed answer to your question.
What is the UML:
The Object Management Group (OMG), a consortium of companies aimed at providing standard languages and technologies, defined a meta-meta modeling language called "The Meta Object Facility" or MOF (http://www.omg.org/mof). A meta-model is a model describing a model or, in other terms, describing the vocabulary (the elements you can use in a model), the syntax (ho they relate each other) and their semantics (what does each entity mean and how its meaning changes in a given context, etc.). A meta-model plays the same role played by Context-Free grammars with respect to the languages they produce. You can thus think at a meta-meta model as a language you can use to define meta-model. This is what the OMG actually did with the UML. The UML language has a meta-model described by means of the MOF in two documents: The UML Infrastructure and the UML Supersturcture (http://www.omg.org/spec/UML).
The UML meta-model has been defined with the aim of been generic enough to cope with the modeling of different systems belonging to different domains. When you define a new UML model you create an instance of the UML meta-model. You could do that for many reasons: to analyse some characteristics of the system, to share some aspects of the system with other stakeholders and so on. However, one of the most important aspects of the OMG vision are model transformations. You can think at a transformation as a set of rules telling an interpreter how to explore a model and produce something else. You can basically transform a model into two different kind of thins, other models (Model2Model, M2M transformations, defined by means of the QVT language) or text such as code or documentation (Model2Text, M2T, transformations defined by means of the MOFM2T Transformation language). So it is VERY IMPORTANT to understand that a UML model is not its diagram. A diagram is just a pictorical representation of the model contents, useful for umans, but not machine readable. You can't apply transformations to a diagram.
The Eclipse Modeling Framework (EMF) is a very powerful (and FREE!) framework implementing all the technologies I have mentioned. A subset of the MOF is implemented in the Eclipse ECORE language. By means of the ECORE the UML meta-model is defined so grafical UML editors (i.e. Papyrus, TopCased, etc.) actually creates XMI representation of the graphically defined UML models conform to the ECORE representation of the UML meta-model. Such representation can be provided as input to transformations engine. The two transformation languages, and related engines, are also available in the EMF with the QVTo plugin and ACCELEO (implementing the MOFM2T transformation language).
As mentioned UML is intentionally generic. However it also provide lightweight extension mechanisms to extends original language vocabulary with domain specific constructs. This can be done by means of stereotypes. A stereotype is a sort of label (actually with meta-attributes) you can attach on model elements to create new entities in the language. You can for instance say in your models some of the classes could be requirements or something else. There are of course some rules, for instance when you stereotype a meta-class you can not violate its original semantics, just reduce it.
SySML is a profile of the UML http://www.omgsysml.org/. A SysML Block is just a UML class stereotyped as Block, a SysML Requirement is just another UML class stereotyped as Block and so on.
Profiling a meta-model like the UML is a quite easy way of creating a sort of DSL (as with stereotypes you add to a more general language some constructs which belong to your domain) which is compatible with the UML (i.e. you can use SysML and UML together). There is another way of creating a DSL which is defining its meta-model by means of the MOF (ECORE). In this case you create a brand new language which is conceptually at the same level of the UML itself.
Many people say UML is just about diagrams because in many cases they do not know what they are talking about. The topic is far more complex, interesting and promising.
UML is a general modelling language that is not specific to any domain whilst the S in DSL stands for Specific. UML is used for modelling systems that can also be represented by multi-purpose programming languages. DSL on the other hand are constrained programming/scripting languages which are specific to a particular domain.
I might have a silly question about DDD:
Are there any disadvatages of DDD generraly? I mean, besides of using it when it is not necessary, or needed. (e.g. small/not complex projets)
Thanks
It is very easy to do it wrong.
Eric Evans has said in a JavaOne presentation that DDD is best applicable when there is a lot of business domain complexity. Moreover, he explicitly states that DDD is not suitable for problems where the is substantial technical complexity but that has little business domain complexity. An example of the later is an embedded system with very simple inputs (possibly independent of the number of states it possesses) while simultaneously presenting a lot of technical complexity (in terms of getting the hardware to work.)
How we go about quantifying a lot or a little, that's an open subject. But the narrative should work as a guideline of when and where DDD is best applicable.
-- edit --
I got the video presentation through Emule, and I've never been able to find that same lecture on youtube or similar video venues.
I found this discussion of DDD in the Microsoft Application Architecture Guide to be helpful in understanding the challenges of that particular style:
As the core of the software is the
domain model, which is a direct
projection of this shared language, it
allows the team to quickly find gaps
in the software by analyzing the
language around it. The creation of a
common language is not merely an
exercise in accepting information from
the domain experts and applying it.
Quite often, communication problems
within development teams are due not
only to misunderstanding the language
of the domain, but also due to the
fact that the domain's language is
itself ambiguous. The Domain Driven
Design process holds the goal not only
of implementing the language being
used, but also improving and refining
the language of the domain. This in
turn benefits the software being
built, since the model is a direct
projection of the domain language.
In order to help maintain the model as
a pure and helpful language construct,
you must typically implement a great
deal of isolation and encapsulation
within the domain model. Consequently,
a system based on Domain Driven Design
can come at a relatively high cost.
While Domain Driven Design provides
many technical benefits, such as
maintainability, it should be applied
only to complex domains where the
model and the linguistic processes
provide clear benefits in the
communication of complex information,
and in the formulation of a common
understanding of the domain.
At an italian conference, I talked about the topic (see these slides).
DDD projects require domain experts that are often expensive to hire, since they hold valuable knowledge (read, if you don't need a domain expert, you don't need DDD).
Moreover DDD requires strong skills on the modeler side. In particular they have to be:
Humble, since they have to accept their ignorance and learn from an expert
Really skilled in OOP
Diligent, since they have to track decisions
Comunicative, since they have to explain the domain to the other devs (even through documentation)
Finding such developers can be much more expensive than expected, since you can really know that they are good at the job after some months of trials.
Martin Fowler in his "PoEA" book has a great discussion of when and what domain logic patterns to use.
For instance, simplest pattern, Transaction Script, involves no domain model.
I'm quite familiar with UML for modeling object-oriented applications. However, I'm not familiar with anything specifically designed for designing and/or modeling procedural, functional, or any other paradigm. How do you design or model applications written in a non-object-oriented language?
Oh golly, there's a blast from the past.
We used to use flowcharts, pseudocode, data flow diagrams, structure charts, Hierarchy-IPO, "coathanger charts" (which are really a variant of flowcharts), Nassi-Schneiderman diagrams. Among others.
Oh, SADT is another one.
SSADM - I think I've still got my certification in a box somewhere...
UML can be used for modeling non-OO languages as well. I use UML for modeling just about anything. To be fair the core of UML is OO focused, but much of the behavior, instance level, and less common structural types work for non-OO languages. However, UML is for design in OO not implementation, your building blocks/objects are just different, modules, or whatnot.
Many of the diagram types mentioned by Charlie Martin have analogous UML representations. Even better it is a model not just a diagram/view.
Example: LISP is not OO based. So create a keyword or stereo type for classes that is function. The attributes are the arguments as it has no state. This is not perfect, but it is the most approachable.
Example: COBOL/JCL is not OO based. Have each PACBASE package be a component and have structural components as your COBOL. Artifacts can be your JCL.
Let fact that UML is broad and loosely defined to your benefit and re-purpose UML parts. You can always formalize it with a UML profile. Where I work this has been a point of discussion for some time. Mainframe programmers do not see OO design and OO-UML as relevant, but it is only partially true in that the core or how far most people go with it is just to the class/structural stuff and use cases, which is OO focused.