Tuesday, May 29, 2007

Software Development Detox Part 3: Join the Conversation

So far we've established that the unsophisticated software solutions tend to be brittle and unreliable due to the following erroneous decisions:
  1. Keeping track of the state of the conversation between the client and the server
  2. Choosing to expose services through messaging interfaces (a.k.a. Remote Procedure Calls)
Today we're going to look into the minimal requirements for establishing the platform for enabling successful implementation of the business computing. We will see how important it is to separate the state of the conversation, that may have transpired between two or more business parties, from the transformations of the state of the participating parties. Also, we'll look into the advantages of abandoning the messaging interfaces when conducting business conversations.

Sustainable Business Strategies

Abandoning the world of software for a moment, let us examine the strategies that facilitate success in the world of business. Experience has shown that short term success is certainly achievable by exclusivity (i.e. by locking customers into some sort of a proprietary business model). However, for achieving any level of sustainability, businesses must, willy-nilly, open up and introduce free choices and embrace diversity.

In order to attain happy equilibrium of a sustainable business growth, one component of the business interaction must be optimized -- conversation. Businesses thrive on open-ended conversation. What that means is that while initially only two privileged parties may begin business conversation, other interested parties should be able to join and participate at any point.

For that to happen successfully, the barriers to entering the stream of conversation must be placed extremely low. In practical terms, anyone interested in joining the conversation should not be expected to learn any arbitrary set of rules, any new language, or any new protocol.

In addition to this fundamental requirement, parties joining the conversation midstream should also be able to easily examine the history. Anyone joining the conversation should be able to immediately gain access to the 'minutes' of all the previous conversations. That way, an interested party could, at their own convenience, examine the minutes and learn about some vital stats of the ongoing business transactions.

These two (the ability to join the conversation at any point in time and the ability to examine what had transpired up until that moment) are the most vital and essential requirements for conducting successful, sustainable business transactions.

Sustainable Business Computing Strategies

When it comes to achieving sustainable levels of business computing, the challenges tend to be even greater. Computing infrastructure and practices, that are being placed between various business parties interested in joining the conversation, serve to raise the barriers to entry.

Still, the promise of information technology is to make those barriers even lower than they tend to be for the non-digital business interactions. And in all truthfulness, that really is the true calling of this technology. So, the question then is: what went wrong?

The simplistic answer to the above question is that someone along the lines made a couple of wrong decisions (see the erroneous decisions listed above) and created a complicated situation resulting in businesses being unable to join interesting and potentially profitable conversations that are happening online.

Our job, then, is to remedy this situation, and to bring the technology back to the level where pretty much any interested business party is capable of easily joining the conversation. Not only that, but any party should qualify for easily examining the history of the conversation by replaying the 'minutes' of what had transpired while they were away.

Simplifying the Medium

In the world of information processing, bits and bytes could represent anything. But in the world of business computing, the medium that is of most interest is text. So in most situations, what is of particular business interest is content that is rendered as text.

Of a much lesser significance, but still figuring rather prominently in the world of business computing, are images. Less prominent media types would be audio and video.

So the viable computing platform that would fully facilitate successful business conversations is mostly focused on the content rendered as text. That content should be marked up in order to achieve certain level of semantic order. But the markup shouldn't be blown out of proportions.

Simplifying the Protocol

Once the medium for exchanging business content is sufficiently simplified, we must make sure that the channels for communicating that content are also fully simplified. Instead of expecting any interested party to learn the intricacies of a foreign language that is unilaterally enforced by the vendor, we must offer a severely restricted list of possible actions that are publicly vetted and extremely non-volatile.

For any resource that the businesses may be interested in, we can safely establish that only four actions would suffice when it comes to maintaining that resource:
  1. Add resource
  2. Remove resource
  3. Modify resource
  4. Fetch resource
The above four-pronged protocol is sufficient for conducting any business conversation. No further elaboration on the business computing protocol should ever be required (there is no need for any kind of messaging interfaces).

Joining the Conversation

When an interested party learns about the ongoing business conversation and wants to join in, all it has to do is fetch the state representation of the resource in question. From that point on, the interested party is free to propose any transition of the state of that resource. In addition to that, the interested party is also free to replay the conversation as it had unfolded prior to joining the conversation.

The above scenario is universal, and it applies across the board. Following this model, we can ensure that any business parties will have a successful transition to participating and contributing to the ongoing stream of business conversations.

Software Development Detox Part 2: Remote Procedure Calls

We've seen in our first detox installment that it is detrimental to maintain the state of the conversation between participating parties. The conversation that may have occurred between the interested parties and a targeted resource may have affected the state of the targeted resource. But that doesn't mean that the various stages of the conversation itself need to be retained.

Today we'll look into another form of software intoxication; this one has to do with how is the conversation implemented.

Typically, when two or more parties get engaged in a conversation, they tend to accomplish successful conversation by sending each other specific messages. For example, if an airplane is approaching the airport, the messaging between the pilot and the control tower gets peppered with code words such as "roger" and "over". That way, the conversation protocol gets established in the attempt to minimize the noise and maximize the signal.

In a loosely coupled world of business computing, free market forces dictate that many solutions providers can compete for the most successful solution. That situation creates a wild diversity of proposed conversation protocols. What's happening is that basically any vendor (i.e. solution provider) is free to come up with a completely arbitrary set of formal rules outlining how is the conversation going to take place. That creates a hell of a noise in the solution space, resulting in brittle and faulty implementations.

The culprit most of the time boils down to the methodology known as Remote Procedure Call (RPC). The remote procedure proposed by the vendor is a completely arbitrary, unilaterally constructed expression that the vendor expects the consumer to learn. In addition, the vendor reserves a unilateral right to change the expression encapsulated at the RPC level, and the consumer has no recourse but to re-learn the intricacies of how to talk to the vendor.

This unfortunate situation creates endless problems and headaches. All the consumers of the proposed vendor services are expected to keep an ever growing inventory of those custom Remote Procedures, and are on top of that left vulnerable to the future changes of that inventory.

Because of that, the effective detox therapy strongly advises against using the RPC model when architecting and designing your software solution. We will see in the next installment what is a much better way to go about accomplishing the robust software architecture.

Saturday, May 26, 2007

Software Development Detox Part 1: State

In the first installment of the software development detox program, I am going to review misconceptions and misunderstandings of one of the most fundamental software concepts -- state.

The problem with understanding state in the context of information processing/software development arises when people fail to recognize and acknowledge that there are two distinct aspects of state in the arena of software development. By bundling up these two aspects, people end up projecting an incorrect picture and consequently paint themselves into a corner by choosing the unsuitable architecture.

I am now going to (temporarily) abandon metaphors (such as 'paint oneself into a corner' etc.) and switch to using simple, albeit somewhat exaggerated examples.

Software Types

In this example, I am going to review a common occurrence of a typical software construct, such as date. Date is an abstraction devised to encapsulate and express human concept of time. In the world of information processing, we use software constructs, such as types, to encapsulate and express abstractions such as calendar date.

Suppose someone offers a software abstraction (i.e. type) called CustomDate. This abstraction is supposedly capable of doing accurate date calculations, and is endowed with certain conveniences. One such convenience being the ability to express, in calendar terms, such human concepts as 'tomorrow', 'yesterday', 'next week', etc.

So we see that this type is capable of certain behavior (such as being able to answer the question 'what date is tomorrow?', etc.) But, in addition to discernible behavior, software types typically also possess state. For example, our CustomDate may possess a state of knowing what date is year-end.

This state may change (different corporations have different year-end dates). And the instance of the type is expected to remember the changed state.

What can you say and how it gets interpreted

Upon acquiring a new software type, such as CustomDate, we will be expected to learn about its capabilities. We are not expected to understand how it is working. We're not even expected to understand all of its capabilities. We are free to pick and choose.

For example, if the CustomDate possesses 50 different capabilities, and all we want from it is the ability to tell us what date is the year-end, we should be able to safely ignore the remaining 49 capabilities.

To violate this basic agreement would result in creating brittle, unreliable software. Here is one fictitious example that illustrates this problem:

If we instantiate CustomDate and assign that instance a handle such as customDate, we should then be able to talk to that instance. If we are only interested in learning about our company's year-end date, we can send a message to our customDate instance, as follows:


In response to receiving that message, the customDate instance will return the actual year-end date to us.

The above described scenario should always yield the same behavior. There shouldn't be any surprises in how an instance of customDate behaves upon receiving the year-end message. If there is even a slightest possibility that the established message may render different, unexpected behavior, our software is not only brittle, but extremely buggy.

By now you may be wondering how could there be a possibility that the above scenario ever yields any different behavior than expected? Let me explain with another example:

We've learned so far that, when dealing with an instance of customDate, we can say year-end and it will be interpreted as a question that reads: "could you please tell me what is the year-end date?" Consequently, the representation of the correct year-end will get rendered and served as a response to our query. We've thus realized that an instance of customDate has state. That state (i.e. the actual value of company's year-end date) is the only state we're interested in when dealing with this software construct.

However, as we've mentioned earlier, this software construct may have 49 other capabilities and states, of which we know nothing. Now, the fundamental principle of software engineering dictates that we are absolutely not required to know anything about any additional, extraneous states and behaviors that a software construct may bring to the table.

Regardless of that prime directive, people who are not well versed in designing software solutions tend to violate this dictum on a daily basis. The way to violate the prime directive would be to introduce certain state/behavior combo that will modify how the question gets interpreted. One can imagine how easy would it be to add a capability to CustomDate which will turn it into a currency conversion utility. This example is admittedly unrealistic and exaggerated, but I chose it to illustrate the foolhardiness of arbitrarily assigning various capabilities to a software construct.

In this example, an overzealous green developer may add a capability to CustomDate that will put it into a "currency conversion" mode. If someone else is using the same instance of CustomDate and puts it into this "currency conversion" mode, that change in its state may modify the behavior of an instance of CustomDate, rendering the response to the year-end question unintelligible.

Let's now run this hypothetical scenario:
  1. CustomDate gets instantiated as a resource on the server

  2. A message arrives from a client asking the resource to convert 100 USD to Canadian dollars

  3. An instance of CustomDate (i.e. customDate) puts itself into the "currency conversion" mode and renders the proper currency conversion

  4. The client then sends a message to customDate asking it for a year-end

  5. The instance renders an answer that corresponds to the value of 100 US dollars at the year-end
The above answer at step 5 comes as a complete shock to the client who asked for a year-end; the client wasn't aware that the instance can be shape-shifting and consequently may not always be returning dates when asked about the year-end.

In other words, what you can say and how it gets interpreted changes based on the state that an instance of the type may be in. A very bad situation, guaranteed to render that particular software program dysfunctional.


We can see from the above example how disastrous it can be to attempt to manage the state of a resource. In our case, we've been managing the state of an instance of
CustomDate, keeping track of when is it a date rendering machine, and when is it a currency conversion machine.

This tracking of the state resulted in the breakage of the working code. If we had abstained from keeping track of the state of the instance, the problems wouldn't have emerged in the first place.

From this we see that the only way to achieve robust and reliable software is to ensure that its constituent components are stateless. No memory of what had transpired during previous conversations should be retained.

However, keep in mind that we must distinguish here two types of states:
  • Entity state
  • Conversation state
It is this conversation state that is troublesome. Entity state is perfectly valid, and should be memorized. In this instance, entity state would be the fact that our company's year-end is October 31.

Keeping track of what transpired as clients have interrogated an instance of a software component, and then retaining that state, is always disastrous. And yet that is how most inexperienced software developers tend to architect and design their software.

Coming up

In the next installment, we'll look more closely into how to architect and design stateless software.