Microservices Expo Authors: Liz McMillan, Elizabeth White, John Katrick, Pat Romanski, Gordon Haff

Related Topics: Open Source Cloud, Java IoT, Industrial IoT, Microservices Expo, Microsoft Cloud, Machine Learning

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.

@MicroservicesExpo Stories
Modern software design has fundamentally changed how we manage applications, causing many to turn to containers as the new virtual machine for resource management. As container adoption grows beyond stateless applications to stateful workloads, the need for persistent storage is foundational - something customers routinely cite as a top pain point. In his session at @DevOpsSummit at 21st Cloud Expo, Bill Borsari, Head of Systems Engineering at Datera, explored how organizations can reap the bene...
The dynamic nature of the cloud means that change is a constant when it comes to modern cloud-based infrastructure. Delivering modern applications to end users, therefore, is a constantly shifting challenge. Delivery automation helps IT Ops teams ensure that apps are providing an optimal end user experience over hybrid-cloud and multi-cloud environments, no matter what the current state of the infrastructure is. To employ a delivery automation strategy that reflects your business rules, making r...
"We started a Master of Science in business analytics - that's the hot topic. We serve the business community around San Francisco so we educate the working professionals and this is where they all want to be," explained Judy Lee, Associate Professor and Department Chair at Golden Gate University, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Cloud Governance means many things to many people. Heck, just the word cloud means different things depending on who you are talking to. While definitions can vary, controlling access to cloud resources is invariably a central piece of any governance program. Enterprise cloud computing has transformed IT. Cloud computing decreases time-to-market, improves agility by allowing businesses to adapt quickly to changing market demands, and, ultimately, drives down costs.
There is a huge demand for responsive, real-time mobile and web experiences, but current architectural patterns do not easily accommodate applications that respond to events in real time. Common solutions using message queues or HTTP long-polling quickly lead to resiliency, scalability and development velocity challenges. In his session at 21st Cloud Expo, Ryland Degnan, a Senior Software Engineer on the Netflix Edge Platform team, will discuss how by leveraging a reactive stream-based protocol,...
We call it DevOps but much of the time there’s a lot more discussion about the needs and concerns of developers than there is about other groups. There’s a focus on improved and less isolated developer workflows. There are many discussions around collaboration, continuous integration and delivery, issue tracking, source code control, code review, IDEs, and xPaaS – and all the tools that enable those things. Changes in developer practices may come up – such as developers taking ownership of code ...
For over a decade, Application Programming Interface or APIs have been used to exchange data between multiple platforms. From social media to news and media sites, most websites depend on APIs to provide a dynamic and real-time digital experience. APIs have made its way into almost every device and service available today and it continues to spur innovations in every field of technology. There are multiple programming languages used to build and run applications in the online world. And just li...
The general concepts of DevOps have played a central role advancing the modern software delivery industry. With the library of DevOps best practices, tips and guides expanding quickly, it can be difficult to track down the best and most accurate resources and information. In order to help the software development community, and to further our own learning, we reached out to leading industry analysts and asked them about an increasingly popular tenet of a DevOps transformation: collaboration.
How is DevOps going within your organization? If you need some help measuring just how well it is going, we have prepared a list of some key DevOps metrics to track. These metrics can help you understand how your team is doing over time. The word DevOps means different things to different people. Some say it a culture and every vendor in the industry claims that their tools help with DevOps. Depending on how you define DevOps, some of these metrics may matter more or less to you and your team.
"CA has been doing a lot of things in the area of DevOps. Now we have a complete set of tool sets in order to enable customers to go all the way from planning to development to testing down to release into the operations," explained Aruna Ravichandran, Vice President of Global Marketing and Strategy at CA Technologies, in this SYS-CON.tv interview at DevOps Summit at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"We are an integrator of carrier ethernet and bandwidth to get people to connect to the cloud, to the SaaS providers, and the IaaS providers all on ethernet," explained Paul Mako, CEO & CTO of Massive Networks, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"Grape Up leverages Cloud Native technologies and helps companies build software using microservices, and work the DevOps agile way. We've been doing digital innovation for the last 12 years," explained Daniel Heckman, of Grape Up in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"NetApp's vision is how we help organizations manage data - delivering the right data in the right place, in the right time, to the people who need it, and doing it agnostic to what the platform is," explained Josh Atwell, Developer Advocate for NetApp, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
"Outscale was founded in 2010, is based in France, is a strategic partner to Dassault Systémes and has done quite a bit of work with divisions of Dassault," explained Jackie Funk, Digital Marketing exec at Outscale, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
"I focus on what we are calling CAST Highlight, which is our SaaS application portfolio analysis tool. It is an extremely lightweight tool that can integrate with pretty much any build process right now," explained Andrew Siegmund, Application Migration Specialist for CAST, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Let's do a visualization exercise. Imagine it's December 31, 2018, and you're ringing in the New Year with your friends and family. You think back on everything that you accomplished in the last year: your company's revenue is through the roof thanks to the success of your product, and you were promoted to Lead Developer. 2019 is poised to be an even bigger year for your company because you have the tools and insight to scale as quickly as demand requires. You're a happy human, and it's not just...
The enterprise data storage marketplace is poised to become a battlefield. No longer the quiet backwater of cloud computing services, the focus of this global transition is now going from compute to storage. An overview of recent storage market history is needed to understand why this transition is important. Before 2007 and the birth of the cloud computing market we are witnessing today, the on-premise model hosted in large local data centers dominated enterprise storage. Key marketplace play...
Cavirin Systems has just announced C2, a SaaS offering designed to bring continuous security assessment and remediation to hybrid environments, containers, and data centers. Cavirin C2 is deployed within Amazon Web Services (AWS) and features a flexible licensing model for easy scalability and clear pay-as-you-go pricing. Although native to AWS, it also supports assessment and remediation of virtual or container instances within Microsoft Azure, Google Cloud Platform (GCP), or on-premise. By dr...
With continuous delivery (CD) almost always in the spotlight, continuous integration (CI) is often left out in the cold. Indeed, it's been in use for so long and so widely, we often take the model for granted. So what is CI and how can you make the most of it? This blog is intended to answer those questions. Before we step into examining CI, we need to look back. Software developers often work in small teams and modularity, and need to integrate their changes with the rest of the project code b...
Kubernetes is an open source system for automating deployment, scaling, and management of containerized applications. Kubernetes was originally built by Google, leveraging years of experience with managing container workloads, and is now a Cloud Native Compute Foundation (CNCF) project. Kubernetes has been widely adopted by the community, supported on all major public and private cloud providers, and is gaining rapid adoption in enterprises. However, Kubernetes may seem intimidating and complex ...