Click here to close now.


Open Source Cloud Authors: SmartBear Blog, Elizabeth White, Jim Scott, Pat Romanski, Liz McMillan

Related Topics: Open Source Cloud, Java IoT, Industrial IoT, Microservices Expo, Microsoft Cloud, IoT User Interface

Open Source Cloud: Article

Abstractness vs Instability: A Neo4j Case Study

Discover Abstractness vs Instability graph

Robert C.Martin wrote an interesting article about a set of metrics that can be used to measure the quality of an object-oriented design in terms of the interdependence between the subsystems of that design.

Here's from the article what he said about the interdependence between modules:

What is it that makes a design rigid, fragile and difficult to reuse. It is the interdependence of the subsystems within that design. A design is rigid if it cannot be easily changed. Such rigidity is due to the fact that a single change to heavily interdependent software begins a cascade of changes in dependent modules. When the extent of that cascade of change cannot be predicted by the designers or maintainers the impact of the change cannot be estimated. This makes the cost of the change impossible to estimate. Managers, faced with such unpredictability, become reluctant to authorize changes. Thus the design becomes rigid.

And to fight the rigidity he introduce metrics like Afferent coupling, Efferent coupling, Abstractness and Instability.

Let's discover all these metrics and how they could be very useful to improve the design of applications. For that let's analyze Neo4j by JArchitect.

Neo4j is a robust transactional property graph database. Due to its graph data model, Neo4j is highly agile and blazing fast. For connected data operations, Neo4j runs a thousand times faster than relational databases.

And here's the dependency graph between all Neo4j jars


Neo4j contains many jars and all of them depend on neo4j-kernel, and to have more details about the weight of using each jar, The DSM (Dependency Structure Matrix) is a compact way to represent and navigate across dependencies between components.


As the matrix shows the neo4j kernel is heavily used by the other jars.

Afferent Coupling:
The number of types outside this project that depend on types within this project.

Let's execute the following CQLinq query to get the afferent coupling of Neo4j jars:

from p in Projects where !p.IsThirdParty select new { p,p.NbTypesUsingMe }


As discovered before the kernel is the more solicited by the other jars.

Efferent Coupling
The number of types outside this project used by types of this project.

from p in Projects where !p.IsThirdParty select new { p,p.NbTypesUsed }


The efferent coupling and afferent coupling could be applied also on packages and types. For example the efferent coupling for a particular type is the number of types it directly depends on. Types where TypeCe is very high are types that depend on too many other types. They are complex and in general have more than one responsibility.

The ratio of the number of internal abstract types (i.e abstract classes and interfaces) to the number of internal types. The range for this metric is 0 to 1, with A=0 indicating a completely concrete project and A=1 indicating a completely abstract project

A = Na / Nc


A = abstractness of a module
Zero is a completely concrete module. One is a completely abstract module.
Na = number of abstract classes in the module.
Nc = number of concrete classes in the module.

Let's take as example the neo4j-kernel-1.8.2 jar and search for all abstract types.

from t in Types where t.IsAbstract || t.IsInterface select new { t, t.NbLinesOfCode }


neo4j-kernel-1.8.2 has 1071 types so the Abstractness is equal to 233/1071 = 0.21755

To increase the abstractness of a project we have to add more abstract classes or interfaces.

The ratio of efferent coupling (Ce) to total coupling. I = Ce / (Ce + Ca). This metric is an indicator of the project's resilience to change. The range for this metric is 0 to 1, with I=0 indicating a completely stable project and I=1 indicating a completely instable project.

I = Ce/(Ce + Ca)
I represent the degree of instability associated with a project.
Ca represents the afferent coupling, or incoming dependencies, and
Ce represents the efferent coupling, or outgoing dependencies

Let's take as example a class where many other classes used it and it not use any other class. In this case this class is considered as stable for the following reasons:

- This kind of class depends upon nothing at all, so a change from a depended cannot ripple up to it and cause it to change. This characteristic is called “Independence”. Independent classes are classes which do not depend upon anything else.

- It's depended upon by many other classes. It became harder to make changes to it. And if we were to change it we would have to change all the other classes that depended upon it. Thus, there is a great deal of force preventing us from changing these classes, and enhancing their stability.

Classes that are heavily depended upon are called “Responsible”. Responsible classes tend to be stable because any change has a large impact.

Let's search for the more responsible types by executing the following CQLinq query

(from t in Types orderby t.NbTypesUsingMe descending, t.NbTypesUsed descending, t.NbBCInstructions descending select new { t, t.NbTypesUsingMe,t.NbTypesUsed})


The Expression class is the most popular one.

Abstractness vs Instability Graph and the zone of pain

To have more details about this graph you can refer to the Robert C.Martin article.

Here's the graph for Neo4j framework


The idea behind this graph is that the more a code element of a program is popular, the more it should be abstract. Or in other words, avoid depending too much directly on implementations, depend on abstractions instead. By popular code element I mean a project (but the idea works also for packages and types) that is massively used by other projects of the program. It is not a good idea to have concrete types very popular in your code base. This provokes some Zones of Pains in your program, where changing the implementations can potentially affect a large portion of the program. And implementations are known to evolve more often than abstractions.

The main sequence line (dotted) in the above diagram shows the how abstractness and instability should be balanced. A stable component would be positioned on the left. If you check the main sequence you can see that such a component should be very abstract to be near the desirable line - on the other hand, if its degree of abstraction is low, it is positioned in an area that is called the "zone of pain".

For example neo4j kernel has many classes depending on it, so it's positioned on the left and in this case it's preferable to be more abstract to leave the orange zone and goes to the green zone.

What's important is to avoid the zone of pain, if a jar is inside this zone, any changes to it will impact a lot of classes and it became hard to maintain or evolve this module.

More Stories By Lahlali Issam

Lahlali Issam Lead Developer at JavaDepend, a tool to manage and understand complex Java code. With JavaDepend, software quality can be measured using Code Metrics, visualized using Graphs and Treemaps, and queried using CQL language, a SQL like to query the code base.

@ThingsExpo Stories
SYS-CON Events announced today that Super Micro Computer, Inc., a global leader in high-performance, high-efficiency server, storage technology and green computing, will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Supermicro (NASDAQ: SMCI), the leading innovator in high-performance, high-efficiency server technology is a premier provider of advanced server Building Block Solutions® for Data Center, Cloud Computing, Enterprise IT, Hadoop/Big Data, HPC and Embedded Systems worldwide. Supermi...
As more intelligent IoT applications shift into gear, they’re merging into the ever-increasing traffic flow of the Internet. It won’t be long before we experience bottlenecks, as IoT traffic peaks during rush hours. Organizations that are unprepared will find themselves by the side of the road unable to cross back into the fast lane. As billions of new devices begin to communicate and exchange data – will your infrastructure be scalable enough to handle this new interconnected world?
"Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Nowadays, a large number of sensors and devices are connected to the network. Leading-edge IoT technologies integrate various types of sensor data to create a new value for several business decision scenarios. The transparent cloud is a model of a new IoT emergence service platform. Many service providers store and access various types of sensor data in order to create and find out new business values by integrating such data.
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome,” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, will show how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants will get the download information, scripts, and complete end-to-end walkthrough of the analysis from start to finish. Participants will also be given the pract...
WebRTC services have already permeated corporate communications in the form of videoconferencing solutions. However, WebRTC has the potential of going beyond and catalyzing a new class of services providing more than calls with capabilities such as mass-scale real-time media broadcasting, enriched and augmented video, person-to-machine and machine-to-machine communications. In his session at @ThingsExpo, Luis Lopez, CEO of Kurento, will introduce the technologies required for implementing these ideas and some early experiments performed in the Kurento open source software community in areas ...
Electric power utilities face relentless pressure on their financial performance, and reducing distribution grid losses is one of the last untapped opportunities to meet their business goals. Combining IoT-enabled sensors and cloud-based data analytics, utilities now are able to find, quantify and reduce losses faster – and with a smaller IT footprint. Solutions exist using Internet-enabled sensors deployed temporarily at strategic locations within the distribution grid to measure actual line loads.
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The Internet of Everything is re-shaping technology trends–moving away from “request/response” architecture to an “always-on” Streaming Web where data is in constant motion and secure, reliable communication is an absolute necessity. As more and more THINGS go online, the challenges that developers will need to address will only increase exponentially. In his session at @ThingsExpo, Todd Greene, Founder & CEO of PubNub, will explore the current state of IoT connectivity and review key trends and technology requirements that will drive the Internet of Things from hype to reality.
There will be 20 billion IoT devices connected to the Internet soon. What if we could control these devices with our voice, mind, or gestures? What if we could teach these devices how to talk to each other? What if these devices could learn how to interact with us (and each other) to make our lives better? What if Jarvis was real? How can I gain these super powers? In his session at 17th Cloud Expo, Chris Matthieu, co-founder and CTO of Octoblu, will show you!
Today’s connected world is moving from devices towards things, what this means is that by using increasingly low cost sensors embedded in devices we can create many new use cases. These span across use cases in cities, vehicles, home, offices, factories, retail environments, worksites, health, logistics, and health. These use cases rely on ubiquitous connectivity and generate massive amounts of data at scale. These technologies enable new business opportunities, ways to optimize and automate, along with new ways to engage with users.
Through WebRTC, audio and video communications are being embedded more easily than ever into applications, helping carriers, enterprises and independent software vendors deliver greater functionality to their end users. With today’s business world increasingly focused on outcomes, users’ growing calls for ease of use, and businesses craving smarter, tighter integration, what’s the next step in delivering a richer, more immersive experience? That richer, more fully integrated experience comes about through a Communications Platform as a Service which allows for messaging, screen sharing, video...
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo in Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal an...
WebRTC converts the entire network into a ubiquitous communications cloud thereby connecting anytime, anywhere through any point. In his session at WebRTC Summit,, Mark Castleman, EIR at Bell Labs and Head of Future X Labs, will discuss how the transformational nature of communications is achieved through the democratizing force of WebRTC. WebRTC is doing for voice what HTML did for web content.
SYS-CON Events announced today that Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, will keynote at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA.
As a company adopts a DevOps approach to software development, what are key things that both the Dev and Ops side of the business must keep in mind to ensure effective continuous delivery? In his session at DevOps Summit, Mark Hydar, Head of DevOps, Ericsson TV Platforms, will share best practices and provide helpful tips for Ops teams to adopt an open line of communication with the development side of the house to ensure success between the two sides.
The Internet of Things (IoT) is growing rapidly by extending current technologies, products and networks. By 2020, Cisco estimates there will be 50 billion connected devices. Gartner has forecast revenues of over $300 billion, just to IoT suppliers. Now is the time to figure out how you’ll make money – not just create innovative products. With hundreds of new products and companies jumping into the IoT fray every month, there’s no shortage of innovation. Despite this, McKinsey/VisionMobile data shows "less than 10 percent of IoT developers are making enough to support a reasonably sized team....
Today air travel is a minefield of delays, hassles and customer disappointment. Airlines struggle to revitalize the experience. GE and M2Mi will demonstrate practical examples of how IoT solutions are helping airlines bring back personalization, reduce trip time and improve reliability. In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect with GE, and Dr. Sarah Cooper, M2Mi's VP Business Development and Engineering, will explore the IoT cloud-based platform technologies driving this change including privacy controls, data transparency and integration of real time context w...
The IoT market is on track to hit $7.1 trillion in 2020. The reality is that only a handful of companies are ready for this massive demand. There are a lot of barriers, paint points, traps, and hidden roadblocks. How can we deal with these issues and challenges? The paradigm has changed. Old-style ad-hoc trial-and-error ways will certainly lead you to the dead end. What is mandatory is an overarching and adaptive approach to effectively handle the rapid changes and exponential growth.