Software development is a young profession, and we are still learning the techniques and building the tools to do it effectively. I've been involved in this activity for over three decades and in the last two I've been writing on this website about patterns and practices that make it easier to build useful software. The site began as a place to put my own writing, but I also use it to publish articles by my colleagues.

In 2000, I joined Thoughtworks, where my role is to learn about the techniques that we've learned to deliver software for our clients, and pass these techniques on to the wider software industry. As this site has developed into a respected platform on software development, I've edited and published articles by my colleagues, both ThoughtWorkers and others, to help useful writing reach a wider audience.

photo of Martin Fowler

photo: Christopher Ferguson

Martin Fowler

A website on building software effectively

If there's a theme that runs through my work and writing on this site, it's the interplay between the shift towards agile thinking and the technical patterns and practices that make agile software development practical. While specifics of technology change rapidly in our profession, fundamental practices and patterns are more stable. So writing about these allows me to have articles on this site that are several years old but still as relevant as when they were written.

As software becomes more critical to modern business, software needs to be able to react quickly to changes, allowing new features to be be conceived, developed and put into production rapidly. The techniques of agile software development began in the 1990s and became steadily more popular in the last decade. They focus on a flexible approach to planning, which allows software products to change direction as the users' needs change and as product managers learn more about how to make their users effective. While widely accepted now, agile approaches are not easy, requiring significant skills for a team, but more importantly a culture of open collaboration both within the team and with a team's partners.

This need to respond fluently to changes has an important impact upon the architecture of a software system. The software needs to be built in such a way that it is able to adapt to unexpected changes in features. One of the most important ways to do this is to write clear code, making it easy to understand what the program is supposed to do. This code should be divided into modules which allow developers to understand only the parts of the system they need to make a change. This production code should be supported with automated tests that can detect any errors made when making a change while providing examples of how internal structures are used. Large and complex software efforts may find the microservices architectural style helps teams deploy software with less entangling dependencies.

Creating software that has a good architecture isn't something that can be done first time. Like good prose, it needs regular revisions as programmers learn more about what the product needs to do and how best to design the product to achieve its goals. Refactoring is an essential technique to allow a program to be changed safely. It consists of making small changes that don't alter the observable behavior of the software. By combining lots of small changes, developers can revise the software's structure supporting significant modifications that weren't planned when the system was first conceived.

Software that runs only on a developer's machine isn't providing value to the customers of the software. Traditionally releasing software has been a long and complicated process, one that hinders the need to evolve software quickly. Continuous Delivery uses automation and collaborative workflows to remove this bottleneck, allowing teams to release software as often as the customers demand. For Continuous Delivery to be possible, we need to build in a solid foundation of Testing, with a range of automated tests that can give us confidence that our changes haven't introduced any bugs. This leads us to integrate testing into programming, which can act to improve our architecture.

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Bromley Mtn, VT (2021)

Data Management

There are many kinds of software out there, the kind I'm primarily engaged is Enterprise Applications. One of the enduring problems we need to tackle in this world is data management. The aspects of data managment I've focused on here are how to migrate data stores as their applications respond to changing needs, coping with different contexts across a large enterprise, the role of NoSQL databases, and the broader issues of coping with data that is both Big and Messy.

Domain-Specific Languages

A common problem in complex software systems is how to capture complicated domain logic in a way that programmers can both easily manipulate and also easily communicate to domain experts. Domain-Specific Languages (DSLs) create a custom language for a particular problem, either with custom parsers or by conventions within a host language.

Books

I've written seven books on software development, including Refactoring, Patterns of Enterprise Application Architecture, and UML Distilled. I'm also the editor of a signature series for Addison-Wesley that includes five jolt award winners.

My Books Page...

Conference Talks

I'm often asked to give talks at conferences, from which I've inferred that I'm a pretty good speaker - which is ironic since I really hate giving talks. You can form your own opinion of my talks by watching videos of some my conference talks.

My Videos Page...

Board Games

I've long been a fan of board games, I enjoy a game that fully occupies my mind, clearing out all the serious thoughts for a bit, while enjoying the company of good friends. Modern board games saw dramatic improvement in the 1990's with the rise of Eurogames, and I expect many people would be surprised if they haven't tried any of this new generation. I also appear regularly on Heavy Cardboard.

My Board Games page...

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All Content

Recent Changes

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Divert the Flow

Thu 20 Jan 2022 10:50 EST

Yesterday Ian Cartwright, Rob Horn, and James Lewis described the Critical Aggregator and how it can metastasize into an invasive form. When a legacy system has such an Invasive Critical Aggregator it's often best, if a little counter-intuitive, to Divert the Flow of data by building a new critical aggregator first. Once this is done, we have far more freedom to change or relocate the various upstream data sources.

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Critical Aggregator

Wed 19 Jan 2022 10:53 EST

Business Leaders often need to make decisions that are influenced by a wide range of activity throughout the whole enterprise. To support this systems often have a what Ian Cartwright, Rob Horn, and James Lewis call a Critical Aggregator: a component whose job is to visit various other systems and pull this information together. A critical aggregator is important, but often metastasizes into an Invasive Critical Aggregator

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Two Phase Commit

Tue 18 Jan 2022 12:42 EST

Continuing his exploration of important patterns to maintain consistency across a cluster, Unmesh Joshi now looks at Two Phase Commit. It's broadly the most familiar approach, but comes with lots of complexities to make it work in practice over unreliable networks.

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Legacy Mimic: a new component that looks like an old one

Wed 12 Jan 2022 10:11 EST

Ian Cartwright, Rob Horn, and James Lewis are also back with the New Year with a couple more articles from Patterns of Legacy Displacement in the funnel for the next couple of weeks. This one describes a Legacy Mimic: a part of the new system designed to make the old system think that nothing has changed.

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Replicated Log: synchronize multiple nodes with a write-ahead log

Tue 11 Jan 2022 10:09 EST

One of the core challenges in a distributed system is keeping the state synchronized across all the nodes, especially when neither the nodes, or the connections between them, are reliable. The core approach to handle with is a replicated log: using the write-ahead log pattern over the cluster. Unmesh Joshi shows how this works using its most common implementation: the Raft protocol.

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Paxos: using two consensus-building phases to handle unreliable nodes

Wed 05 Jan 2022 10:53 EST

Unmesh Joshi is ready to start the New Year with a few more of his Patterns of Distributed Systems. With this one he attempts the tricky task of explaining Paxos. This is a well-known protocol developed by Leslie Lamport, for nodes to reach a reliable consensus when both they, and the network, are prone to unexpected failure. Although it's well-known, it's also notoriously difficult to understand, indeed we had considerable difficulty getting our heads around it. We hope this description makes it a bit easier for those who follow us.

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