111 of 119 people found the following review helpful
on December 25, 2003
If you have even been involved in a software project (a) as a developer and did not know what the end product is going to be used for or how it will be used or (b) as an architect who spent countless hours with your stakeholders and domain experts trying to figure out how to go about architecting your application, then you should read this book. Read it again after you have read it for the first time. This book is packed with pointers, information, tips, how-tos, "down to earth" practical samples, and even conversational examples that one could have while gathering requirements. Evans in his book fills a wide gap that we all tend to come across while designing software applications.
There are many software engineering processes out there, and each one tries to tackle the complexities of designing software applications for a given domain in its own way. Evans recognizes the tools and the processes that are popular in the industry, UML, Agile, and focuses on some aspects of the software engineering process that we tend to miss. He starts the book by talking about the importance of creating and having a Ubiquitous Language. There is a similar concept in the RUP, but not emphasizes as much - or at all. Evans goes into a great detail on why, from the inception of a project, it is important to have a common language and gives many pointers on what makes up the Ubiquitous Language for each project:
"Use the model as the backbone of a language. Commit the team to exercising that language relentlessly within the team and the in the code. Use the same language in diagrams, writing, and especially speech."
Parts II-IV of the book put domain-driven design in perspective, and show the reader thru examples and patterns, architectural patterns, design patterns and process patterns, the importance of having a consistent model that maps to the domain and how to go about achieving such model. In an essence, "Model-Driven Design discards the dichotomy of analysis model and design to search out a single model that serves both purposes".
Part II of the book, introduces the building blocks of a Model-Driven Design. This section, as with the others, takes popular patterns from the Gamma, Flower, or others and applies them to the topic at hand - Model-Driven Design. In that aspect, the reader can easily follow the text and relate to topic at hand. Evans uses the ever-popular Model-View-Controller (MVC) design pattern to get things going in part II. He then goes off to explain why the layered architecture approach is an important aspect of a Domain-Driven Design and how it would makes things simpler:
"[Layered Architecture] allows a model to evolve to be rich enough and clear enough to capture essential business knowledge and put it to work."
The author then goes into great detail in explaining the elements that express a model:
1) Entities: An object that is tracked thru different states or even across different implementations.
2) Value Objects: An attribute that describes the state of something else.
3) Services: Aspects of domain that are expressed as actions or operations, rather than objects.
4) Packages: Organize the objects and services.
What do you want to do after you have designed such elements? The creation and life cycle management of objects are discussed next in this book. Three patterns, mostly from the Gamma book, are used to manage the life cycle of objects:
Aggregates represent the hierarchy of objects or services and their interactions. Factories and Repositories operate of Aggregates and encapsulate the complexity of specific life cycle transitions.
Part III of the book talks about the things developers and architects need to do to achieve a Supple Design. Refactoring over and over represents the topic in this section:
"Each refinement of code and model gives developers a clearer view"
The author talks about a breakthrough point during the design that the "designers see the light" and both the domain experts and the designers, after many iterations, have finally come to this higher level of understanding of the domain and the value of refactoring exponentially increases after that.
Part IV of this book talks about a very important topic that we all have struggled with one time or another: the ability of the model and the modeling process to scale up to very complicated domains. It is great that we can model a small domain, but one goes about modeling an enterprise, which is most likely, too complex to model as a single unit? Low-coupling and high cohesion still applies here, but the goal is to not loose anything during the integration process. The author goes in to a great detail in this part to emphasize that even in large circumstances such as modeling an enterprise, every decision must have a direct impact on system development. Three different themes are covered in this section in order to assist with modeling of large units:
1) Context: the model has to be logically consistent throughout, without contradictory or overlapping definitions. For this theme, the author introduces the concept of a Bonded Context- a way that relationship to other context are defined a overlapping is then avoided.
2) Distillation: Reducing the clutter and focusing attention appropriately.
3) Large-scale Structure. The concept of Responsibility layers are introduced
In summary, Evans did a great job in writing this book, and filling it with useful ways of designing and architecting software applications that target a domain, which in most cases we do not know much about.
150 of 166 people found the following review helpful
on June 25, 2004
I bought this book due in part to the glowing reviews here on Amazon so I feel a duty to inject a bit of skepticism, now that I've read it.
5 stars for a technical book indicates to me a book of profound quality that really breaks through with penetrating insights -- The kind of book that makes me think, "Wow, this book has really brought my development practice into a renewed, sharper focus." It doesn't necessarily have to provide radically new material, but it does have to package whatever material it contains in a way that causes the gears in my head to shift around and reorganize themselves. Design Patterns is such a book. XP Explained is such a book. I don't think this one qualifies.
Some good points: The author makes a good case for agile development/extreme programming (close relationship with the customer, unit tests, refactoring...). He seems to believe there may be a tendency to over-emphasize the importance of code and to neglect design in such practices, which may or may not be true in industry at large. But in any case, his major thesis is that it is also important to consider the overall domain model and how well-aligned it is to the goals of the business. He proposes developing a common ("ubiqitous") language between developers and business users, and to unify the various traditional views of a software system (requirements, analysis model, design model, etc..) into one. The advice is quite wholesome and will hopefully promote bringing some harmony between the agile camp and the adherents of high-ceremony approaches such as RUP and CMM.
Some bad points: The book is rather wordy, and a lot of common-sense ideas are repeated at length. I don't feel that the patterns in the book are much more than re-statements of basic principles of OO design. I am not convinced that giving every possible variation on OO programming a fancy name is particularly helpful. Most of the patterns in this book come down to "produce a clean design that removes duplication and attempts to match the business domain." If you're new to OO, I suggest you'd be much better off reading some other books, such as GoF's Design Patterns, Fowler's Refactoring, Page-Jones' Object-Oriented Design in UML, and Kent Beck's XP Explained.
I give this book 3 stars because it's not a bad thing to read a book that makes you think about the importance of the business domain when programming. It's true that this emphasis, while fairly basic, does get lost in a world where specific technologies dominate good design and common sense. I don't think this book can really hurt -- although I have found the "declarative" approach it mentions can be very dangerous in inexperienced hands and can produce utterly unmaintainable code. It's not a bad effort, but it's not an earth shattering revelation either.
52 of 60 people found the following review helpful
on September 25, 2003
I think that this book along with Robert Martin's "Agile Software Development, Principles, Patterns, and Practices" and Martin Fowler's "Refactoring" are perhaps the three most fundamental prerequisites for making the leap in knowledge and maturity from object-oriented programming to true proficiency in object-oriented design. The books from Martin and Fowler cover the software solution design space and the core principles and patterns for making code that is resilient to change and easy to maintain. Eric Evans book covers the problem domain space and the abstraction skills that free programmers to "break out of the box" of the implementation domain and solution objects into the critical area the business domain and corresponding domain objects.
I once led a young software team and tried to convey the need for and essence of these skills to them, but I didnt have the right words and terms to do it for their level of experience. I wish this book had been available to me then because I think it would have made a real difference for that team.
13 of 13 people found the following review helpful
on September 16, 2004
In Domain-Driven Design, Evans describes a set of patterns that capture exactly what both MDA and AOP attempts to be a solution to. Evans approach is elegant, yet realistic. Unlike other model-focused approaches, he has a good focus on lessons learned from agile software development like extreme programming, and explains how domain modeling fits in with testing-driven development, iterative and incremental development, and refactoring.
I have one big gripe with this book, however. It is too long. Everything in the book is useful to me, but I would like to see more people read the parts of the book that are relevant to them. If the book had a thinner companion version or a reading guide for people who were in a hurry in the introduction it would be perfect. As it is, I cannot recommend it to "coders" or business analysts, only to software architects and modelers.
56 of 68 people found the following review helpful
on July 22, 2009
Format: HardcoverVerified Purchase
In italian we have this fun saying" "Dalle stelle alle stalle" which can be translated to "From the stars to the stables" meaning going from brilliant and promising beginnings to a low and humbling ending.. well I find that it describes perfectly this book. Writing a bad tech book is already a mortal sin without making things even worse by raising reader's expectations with a pompous title like "tackling complexity in the heart of sofware". The only thing that this book tackles is the patience of the reader forced to wade through a sea of fluff to find the few interesting ideas that are actually present. It's not that this book contains zero value, it does present some interesting ideas, but the level, usefulness and impact of these ideas are barely enough to justify a series of blog posts, not a book and certainly not a 500 pages book! Add to this lack of structure and organization, continuous repetitions and a pompousness beyond imagination with the annoying habit of continually uppercasing or bolding the "important ideas" and inventing pompous sounding name for simple concepts in the vain attempt to hide their triviality and you will have an idea of the torments that await you if you buy this book and attempt to read it.
The truly facinating question is: "how did this barely decent series of blog posts manage to get so popular and receive respect and good reviews?". I think the answer lies on its cover. It's like with modern art and abstract painting... some guy puts together something kind of original or vaguely interesting or just plain strange, a couple of critics start praising its outstanding aestetics and deep meaning for personal reasons of just as a way to praise themselves who are the only ones able to discern such beauty and meaning , they present the work in an elegant and "important" location and well.. the rest of us deep inside still think it 's fried air, but we still go to the exhibit and dare not say so, since well.. if it's so higly regarded there must be a reason, and maybe it's just that I am not good enough to get it... That's why the best qualification for this book and the attitude it promotes "kandinskian". A (hopefully) failed attempt to transfer to software design and development the horrors of art criticism.
And to the author and whoever shares his love for pompous sounding words and names (or as he would say it: "UBIQUITOUS LANGUAGE") I would advise to reflect on this Feynman quote:
"You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing -- that's what counts. I learned very early the difference between knowing the name of something and knowing something."
11 of 11 people found the following review helpful
on April 9, 2009
"The defining characteristic [of domain-driven design] is a priority on understanding the target domain and incorporating that understanding into the software. Everything else flows from that premise."
Eric Evans argues that developers must not just understand the business ("domain") concepts in an application, but must also be able to communicate with domain experts to elucidate and refine concepts that are not obvious from the beginning. The "domain model" that emerges from this process must always be reflected in the code as much as possible (and separated from infrastructure or even non-core domain code).
The author deserves credit for asserting (back in 2003, when this might have been less widely recognized) that proper design and iterative development are not mutually exclusive, and that the design of an application is in fact unlikely to be good without iterative development.
The book contains a good mix of abstract discussion mixed with examples (including diagrams and dialogs between developers and business experts). On the other hand, there is not much discussion (or good solutions) on how to implement the practices the author is advocating (e.g. having model objects do database queries rather than delegating this to a service layer).
The author relies a lot on UML diagrams (especially class diagrams) to illustrate domain models, though the few examples where he uses custom, non-UML diagrams to illustrate behavior are far more interesting.
In the end I don't think I got more out of the book than if it had been summarized in a blog post. In particular, the "refactorings" and "patterns" didn't seem to add much to what I had read elsewhere, and some parts of the book seem a bit repetitive, even if otherwise well written.
13 of 14 people found the following review helpful
on April 20, 2005
This book has subtly but deeply influenced the way I think about software projects. One of the key concepts is 'ubiqitous language'-- basically making sure that everyone involved with modeling the domain uses the same vocabulary-- and now I find myself feeling much more justified in pushing for this in meetings. That's the really great thing about these types of books, if you ask me. Like Martin Fowler's 'Refactoring', DDD codifies a lot of what an experienced developer already knows and does...The key is the codification, which provides much-needed legitimacy in the case of domain modeling, which is often trumped by technology obsession in our industry.
I give this 4 stars instead of 5 only because I prefer a more industry-oriented, less academic style -- that of Ted Neward, for example. I get the feeling Evans, like Fowler, is trying to rise above the practical level to something more general and permanent, but personally I like things in the "ubiqitous language" of enterprise Java as I'm practicing it today.
12 of 13 people found the following review helpful
on July 9, 2004
Even if we're geeks from birth, and grow up playing with tinker toys or legos and graduate to software or electronics and then make it through engineering or software school with high marks, most of us never really encounter extremely complex problems until we are employed in industry. The result is that we are pushing thirty before we encounter problems that we can't simply jump into and starting building the solution for. We end up approaching every problem with tools and materials in hand, neglecting the important problem space analysis that must come first. Evans does a superb job of explaining how OO analysis of the problem domain leads to natural, sensible reflections in the solution space. It may be that there are too many words in this book, and it may be that the ordering is a little off, but the message is dead on, and shouldn't be ignored by anybody who's serious about solving very complex problems with software. If software is part art and part science, this book describes the art very well.
14 of 16 people found the following review helpful
on August 22, 2007
Format: HardcoverVerified Purchase
This book presents some interesting ideas for data modeling and lifecycle management, but does not provide enough implementation details to turn those ideas into reality. Many people are attempting to do so, and their ideas turn up in the dozens with a Google search, but no one seems to have figured out a real-world implementation yet. I may have given this 4 or 5 stars if I was convinced that the ideas were practical. I assume Evans has implemented his own ideas before, so I'm left wondering why he's not sharing the code.
In particular, the Repository and Aggregate patterns interests me, but there are many problems that arise when trying to implement a Repository that can handle saving and updating entire Aggregates while keeping the Entities isolated from the persistence mechanism. This is a topic for a tech blog, and in searching the 'net, plenty of them are discussing it. No one seems to have answered the implementation question, though.
The book is also a bit repetitive and verbose. I didn't find the sections on ubiquitous language very helpful. Engineers and non-engineers don't approach problems the same way, common language or not. I didn't feel that added much to the technical design discussions that followed.
If I ever figure out a practical implementation of the ideas, I may come back and give the book another star.
10 of 11 people found the following review helpful
on September 2, 2005
As a developer it is quite easy to take the requirements, do some design and go off and code and come back with a product only to find out later, that the customer really did not want the developer's interpretation of the requirements. This book is more than a reminder of this notion, but also lays out some examples of real experiences of deriving the model. Software engineering is one of those areas that require the trade of knowing the technical development skills and also acquiring great understanding of the domain to be abstracted, developed and made into something computerwise tangent. This is a great book for developers, business analysts, project managers, and anyone in the software business. While others may not regard this book as one of the classics, I find this book an important reminder lest we forget why we are developing the software and the perspective to take while working with the customer.
Thank you, Eric for such a work.