Click here to close now.

Welcome!

Microservices Journal Authors: Liz McMillan, Lori MacVittie, Ruxit Blog, Roger Strukhoff, Carmen Gonzalez

Related Topics: Open Source, Java, XML, Microservices Journal, .NET, AJAX & REA

Open Source: 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

neo4j1

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.

neo4j6

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 }

neo4j2

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 }

neo4j3

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.

Abstractness
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

Where:

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 }

neo4j4

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.

Instability
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})

neo4j5

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

AbstractnessVSInstability

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
SYS-CON Events announced today that Vicom Computer Services, Inc., a provider of technology and service solutions, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. They are located at booth #427. Vicom Computer Services, Inc. is a progressive leader in the technology industry for over 30 years. Headquartered in the NY Metropolitan area. Vicom provides products and services based on today’s requirements...
SYS-CON Events announced today that Blue Box has been named “Bronze Sponsor” of SYS-CON's DevOps Summit New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Blue Box delivers Private Cloud as a Service (PCaaS) to a worldwide customer base. Built on a technology platform leveraging decades of operational expertise in cloud and distributed systems, Blue Box Cloud is a managed private cloud product available in both hosted and on-prem versions. Each Blue Box ...
Lacking the traditional fanfare associated with any technology that can use the word "container" or mention "Docker" in its press release, Ubuntu Core and its new Snappy system management scheme was introduced late last year. Since then, it's been gaining steam with Microsoft and Amazon and Google announcing support for the stripped-down version of the operating system. Ubuntu Core is what's being called a "micro-OS"; a stripped down, lean container-supporting machine that's becoming more pop...
This is a no-hype, pragmatic post about why I think you should consider architecting your next project the way SOA and/or microservices suggest. No matter if it’s a greenfield approach or if you’re in dire need of refactoring. Please note: considering still keeps open the option of not taking that approach. After reading this, you will have a better idea about whether building multiple small components instead of a single, large component makes sense for your project. This post assumes that you...
The stack is the hack, Jack. That's my takeaway from several events I attended over the past few weeks in Silicon Valley and Southeast Asia. I listened to and participated in discussions about everything from large datacenter management (think Facebook Open Compute) to enterprise-level cyberfraud (at a seminar in Manila attended by the US State Dept. and Philippine National Police) to the world of entrepreneurial startups, app deployment, and mobility (in a series of meetups and talks in bot...
This digest provides an overview of good resources that are well worth reading. We’ll be updating this page as new content becomes available, so I suggest you bookmark it. Also, expect more digests to come on different topics that make all of our IT-hearts go boom!
SYS-CON Events announced today the DevOps Foundation Certification Course, being held June ?, 2015, in conjunction with DevOps Summit and 16th Cloud Expo at the Javits Center in New York City, NY. This sixteen (16) hour course provides an introduction to DevOps – the cultural and professional movement that stresses communication, collaboration, integration and automation in order to improve the flow of work between software developers and IT operations professionals. Improved workflows will res...
I woke up this morning to the devastating news about the earthquake in Nepal. Sitting here in California that destruction is literally on the other side of the world but my mind immediately went to thinking about my good friend Jeremy Geelan. See Jeremy and his family have been living in Kathmandu for a while now. His wife, in fact, is the Danish Ambassador to Nepal!
SYS-CON Events announced today that B2Cloud, a provider of enterprise resource planning software, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. B2cloud develops the software you need. They have the ideal tools to help you work with your clients. B2Cloud’s main solutions include AGIS – ERP, CLOHC, AGIS – Invoice, and IZUM
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch ...
SYS-CON Events announced today that MangoApps will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY., and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MangoApps provides private all-in-one social intranets allowing workers to securely collaborate from anywhere in the world and from any device. Social, mobile, and eas...
There is no doubt that Big Data is here and getting bigger every day. Building a Big Data infrastructure today is no easy task. There are an enormous number of choices for database engines and technologies. To make things even more challenging, requirements are getting more sophisticated, and the standard paradigm of supporting historical analytics queries is often just one facet of what is needed. As Big Data growth continues, organizations are demanding real-time access to data, allowing immed...
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on T...
One of the most frequently requested Rancher features, load balancers are used to distribute traffic between docker containers. Now Rancher users can configure, update and scale up an integrated load balancing service to meet their application needs, using either Rancher's UI or API. To implement our load balancing functionality we decided to use HAproxy, which is deployed as a contianer, and managed by the Rancher orchestration functionality. With Rancher's Load Balancing capability, users ...
There are 182 billion emails sent every day, generating a lot of data about how recipients and ISPs respond. Many marketers take a more-is-better approach to stats, preferring to have the ability to slice and dice their email lists based numerous arbitrary stats. However, fundamentally what really matters is whether or not sending an email to a particular recipient will generate value. Data Scientists can design high-level insights such as engagement prediction models and content clusters that a...

As a company making software for Continuous Delivery and Devops at scale, at XebiaLabs we’re pretty much always in discussions with users about the benefits and challenges of new development styles, application architectures, and runtime platforms. Unsurprisingly, many of these discussions right now focus on microservices on the application side and containers and related frameworks […]

The post May. 3, 2015 10:00 AM EDT  Reads: 1,757

SYS-CON Events announced today the IoT Bootcamp – Jumpstart Your IoT Strategy, being held June 9–10, 2015, in conjunction with 16th Cloud Expo and Internet of @ThingsExpo at the Javits Center in New York City. This is your chance to jumpstart your IoT strategy. Combined with real-world scenarios and use cases, the IoT Bootcamp is not just based on presentations but includes hands-on demos and walkthroughs. We will introduce you to a variety of Do-It-Yourself IoT platforms including Arduino, Ras...
What’s hot in today’s cloud computing world? Containers are fast becoming a viable alternative to virtualization for the right use cases. But to understand why containers can be a better option, we need to first understand their origins. In basic terms, containers are application-centric environments that help isolate and run workloads far more efficiently than the traditional hypervisor technology found in commodity cloud Infrastructure as a Service. Modern operating systems (Linux, Windows, e...
The cloud has transformed how we think about software quality. Instead of preventing failures, we must focus on automatic recovery from failure. In other words, resilience trumps traditional quality measures. Continuous delivery models further squeeze traditional notions of quality. Remember the venerable project management Iron Triangle? Among time, scope, and cost, you can only fix two or quality will suffer. Only in today's DevOps world, continuous testing, integration, and deployment upend...
Financial services organizations were among the earliest enterprise adopters of cloud computing. The ability to leverage massive compute, storage and networking resources via RESTful APIs and automated tools like Chef and Puppet made it possible for their high-horsepower IT users to develop a whole new array of applications. Companies like Wells Fargo, Fidelity and BBVA are visible, vocal and engaged supporters of the OpenStack community, running production clouds for applications ranging from d...