Integrating Requirements Deliverables

Some of the requirement Deliverable integration possibilities have been touched on in the previous postings. Listed together, they are:

- Process Maps identify all steps of a process, and a Process Step can indicate when a Use Case is used in the Business.

- Use Cases can include the Declarative Requirements for the Information System/Solution.

- A Data Model will document all data items used within the scope of a set of Use Cases, and is cross-referenced in the Use Case for the data items used by the latter.

- Business Rules can also be documented across the scope of the Business being analyzed, including both the set of Use Case and the overall Process Map, as a Business Rule may be invoked at different points and times with the Business Operations. Use to date has shown they can then best cross-referenced in:
o In the Use Cases whose execution is impacted by one or more Business Rules
o In Process Maps at Decision Points, as Business Rules may play a role in deciding which path within a Map should be followed in any one execution of the Process

I have a diagram showing the relationships, but my blog site does not want to accept an upload of it. I will keep trying, but in the meantime, contact me at dwwright99@hotmail.com and I will send you the diagram (as a bmp file).

Business Rules

As a concept, Business Rules are not new, to the Business or IT; what is new is the focus on separating them from other forms of documentation so they can better defined and managed. Business Rules are similar to Process Models/Maps in that they are subject to more frequent change than other aspects of the business, frequently enough that if rules are hard-coded in an Information System, the effort and elapsed time to change the system can be too large to be tolerated by the business over time.
So, just as generic Process ‘systems’ are emerging to support rapid process change, so are Business Rule Systems and Vendors that support Business Rule Management and Change independently of the information systems that uses them.

What is a Business Rule?
A business rule is a statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or influence the behavior of the business. The business rules that concern (an Information Systems) project are atomic – that is, they cannot be broken down further.
“Defining Business Rules ~ What Are They Really?”, Copyright ©2001, the Business Rules Group.

I would add the word ‘declarative’ to the definition, as in “a business rule is a declarative statement that defines…” emphasizing that Business Rules do not imply and process, procedure, flow or other ‘system’ structure. If Business Rules are separately defined and managed, they can then be used as needed by any process/procedure/flow that needs a rule’s guidance or constraint.

The paper with the above definition is available at http://www.businessrulesgroup.org/first_paper/br01ad.htm
It includes an example case study of a fictitious car rental company with many defined business rules; here is a sample:

Rental reservation acceptance
- If a rental request does not specify a particular car group or model, the default is group A (the lowest-cost group).
- Reservations may be accepted only up to the capacity of the pick-up branch on the pick-up day.
- If the customer requesting the rental has been blacklisted, the rental must be refused.
- A customer may have multiple future reservations, but may have only one car at any time.

So, please go read that article at the Business Rules Group website (I want to avoid any charges of plagiarism of that site on my site).

To ensure that Business Rules are meaningful and clear, they are always based on a defined set of ‘Terms and Facts’, which are used as the language of the Rules. Terms from the above examples include rental request, car group, reservation, branch, and customer. An example of a fact would be "a customer may have multiple future reservations": it’s when you add the constraint "but may have only one car at any time" that you have a rule, using that fact and the relevant terms.

Defining terms and facts can also be seen as a role of an Entity-Relationship Data Model, such that the Entities/Attributes and Relationships of such a Data Model can readily be used as the Terms and Facts for defining Business Rules. The two types of models are different in some ways, but they are similar enough that if you have both, you can easily use one to drive the creation of the other.


So, now we have covered all the Requirements formats that I commonly use:
· Declarative Requirement Statements
· Use Cases
· Data Models
· Process Models
· Business Rules

… and I have already touched on some aspects of how these formats can be inter-related and integrated. I will review all those and add some more aspects in my next post on Integrating Requirements Deliverables.

Process Models - are they bad for Requirements?

I am not aware of the origin of Process Models as we see them today, but their profile was certainly raised by Hammer and Business Process Re-engineering; you certainly had to define your Business Process before improving/re-engineering it. For myself, the one aspect of Process Models that does not get enough attention is defining & understanding the Events in the business environment (external or internal) that kick-off the execution of a Process; know your Events, as they come in handy in many ways when defining Information System Requirements

As a format for documenting Information System Requirements, process models can have a negative impact on the resulting system. The process as it exists at the time of documentation has often been ‘hard-coded’ in the delivered computer system; when the process needs to change, the system cannot support a different process, and the business starts to adapt or create work-arounds to get the work done despite the constraints of the system.

This situation occurs frequently because it is not recognized that some aspects of the business are less stable than others. It has been shown that the process of a business, especially the order of separate steps, is the least stable aspect of a business; at the other end of the scale, the data items and their definitions as used by a business are the most stable aspect of that business. In between the two ends of the scale fall things like specific procedures (units of work) and business rules.

So, automation of the current business process should not be an Information System Requirement. In fact, more generic process and workflow software have been developed over the years to specifically support rapid change in process, adding or changing or re-ordering process steps as needed.

Where Process Models play a role in documenting Information System Requirements is to provide a context for Use Cases. Most steps in a process map will state that some work is done in that step, before the process flow continues; often this work involves use of an Information System, which can be documented as a Use Case. As stated in earlier posts, the Use Case then provides context for Declarative Requirement Statements, as well as a cross-reference to data items and their definitions in a Data Model.

Just a few years ago, this would have been the last ‘format’ that would have been described in this document. However, a new emphasis on methods and formats for documenting Business Rules has recently emerged, the topic for my next posting.

Data Requirements

Data Models are used to define the data needed for an Information system to use and/or control, and often form the basis for the definition and creation of databases. The most common format used to capture data requirements is the Entity-Relationship Diagram, which I believe originated with Clive Finkelstein and was most popularized by James Martin’s Information Engineering Methodology.

A Web Search on Entity-Relationship Diagrams or on Data Models will return thousands of hits, as I think that Data Models as a requirements format are more popular than even Use Cases. Here are two interesting links I found today:

1) Data Modeling: Finding the Perfect Fit
An Introduction to Data Modeling
by Tim McLellan
Copyright 1995. All Rights Reserved.
http://www.islandnet.com/~tmc/html/articles/datamodl.htm


2) Applied Information Science
(Data) Modeling Methodologies
http://www.aisintl.com/case/method.html


In my use of data models for Requirements, the main component is the Data Entity, a subject of interest to the Business, associated by the business relationships between them. Each entity contains data items/attributes that relate to or describe the Entity. Each attribute belongs only to one Entity, so duplication of Requirements is reduced.

Entity-Relationship data models are also commonly classified as ‘Conceptual’ or ‘Logical’, in that they are intended to communicate the data requirements of the Business. Such models can then be transformed into a ‘Physical’ Data Model that is used to design a database.

If a Data Model is used in conjunction with Use Cases, the latter’s data items can be defined by a cross-reference to the Data Model. As a result, a data item used in multiple use cases will be defined only once, eliminating duplication and inconsistency.

Use Cases

I am probably a relative new-comer to use cases, after working in analysis and requirements through Structured Analysis and Design in the eighties, and Information Engineering in the nineties. I found one author’s description of them almost aesthetically appealing, that each one is a case (or example) of the use of a system.

After that, I have seen many variations and permutations and various ‘uses’ of use cases; either that is a testament to their flexibility, or a condemnation of their vagueness. If you are new to Use Cases, be aware that different flavors of use cases are out there, being promoted and being used. When I am feeling the need for some rigor or consistency, I always go back to Alistair Cockburn (pronounced ‘coburn’) at http://alistair.cockburn.us/

Overall, I have seen and used two basic types of use cases:

- A multiple-step interaction between Actor and System, which relates to user interface design, and capturing the required functionality the system must provide to support the interaction. I saw this a lot when working with co-workers who were OO designers and programmers.

- A single step or occurrence format, where an Actor initiates the use case, which is provided some input and/or pre-conditions, and it executes a set of actions (calculate something, retrieve or store something else) that produces a result of interest to the Actor. (There may be multiple Actors, too.) The set of actions that are first defined are those that will normally execute, if no exceptions or other variations occur. I call this the ‘happy path’, as I am sure some author or instructor called it that, but I can’t recall who. However, if it is known that one or more exceptions/variations from the ‘happy path’ could occur (due to certain input values or combinations of pre-conditions), these are documented as alternative paths. Creators of these types of use cases don’t like to see path selection in their use cases, no “IF-THEN-ELSE” statements; use your alternatives instead.

Finally, both of the above types differentiate between the use case itself as the definition or template of the ‘use of the system’, and Scenarios, which are specific instances of the use case given one set of possible input values or pre-conditions; changing the input values produces another scenario, so a large number of scenarios could be defined for one use case, all of which will help the Testers of the information system developed based on the use case(s).

As you might expect by now, I mainly use the second type of use case as part of documenting Information Systems Requirements. They are extremely valuable as, if nothing else, a widely-accepted format for documenting the results of Analysis; anything that effectively assists in communicating Business Requirements to one or more audiences is something that should be used(!).

Now, they are not perfect, and they are not the ultimate format for documenting Requirements… they are only one format of many (five at last count). One issue I had with use cases early on was identifying them in the first place: what was the scope of each use case? How many use cases do you need? There will definitely be more than one. What I can say now is that one way use cases can be identified is by there relationship with Process Models, and I will describe this in a future post.

However, once you do have a set of use cases defined that cover the scope of the business you are analyzing, you can use them to organize the Declarative Requirements Statements I described in my last posting. I often start an Analysis effort by creating a list of High-Level Requirement Statements based on initial discussions with the business subject matter experts; if the these people want a new or enhanced system, they will tell you what they want from that system, which you can capture as Declarative Requirement Statements.

Once I have moved ahead to capture the necessarily detailed description of the business in use cases, I then allocate those Declarative Requirement Statements to the use cases that will actually support the Requirements (if you end up with Requirements that don’t match up to any of your use cases, you might be missing some use cases.) Detailed analysis will also support the definition of more Requirement Statements, again associated with particular use cases.

It might be argued that the detail provided in a use case supersedes the need for Requirement Statements, but I believe they still play an important role in communicating the essence of the use case. Designers/Developers will look to the use case detail for their understanding of the Requirements, but the Requirement Statements are often preferred by Testers as documentation of what they must test, and the Statements provide trace-ability from the Analysis through Design/Development to Testing.

So to this point, we have covered Declarative Requirement Statements and Use Cases, including how the two can be associated with each other… it must be time to discuss Data Requirements… in my next post.

Declarative Requirement Statements

The Declarative Requirement Statement format is a direct assertion of one “...property that is essential for an IT system to perform its functions.” They are ‘declarative’ in that they do not imply any order or flow upon the information system. Such statements are usually part of a larger group or list of Requirement Statements, and can be documented at various levels --- from High-Level Requirements that are often documented first in a project, to detailed statements used as input to Design and as the source of Test Cases.

The common structure is: “…the System must .”

Variations on this structure include:

• Referring to the “Solution’ instead of ‘System’, as an information or other type of ‘System’ is not always what is needed to meet the Requirements of the business.
• Variations on the verb ‘must’, such as ‘shall’ or ‘will’; a ‘must’ statement is often interpreted as a mandatory requirement, while statements using other verbs mean the requirement is optional or ‘nice-to-have’. If multiple verbs are used in a set of Requirement Statements, the specific meaning of the use of each verb should be clearly defined.

Examples:

“The System will provide security that a Manager can only view salary data for their own reporting staff.”

“The System will calculate the monthly payment for a loan application, given the
• Interest Rate,
• the Amount Borrowed,
• and the Number of Payments & Payment Frequency”

Presenting large numbers of Requirement Statements can be a challenge, and grouping them by common attributes is one means of organizing the statements; one very common classification is the grouping of requirements as Functional or Non-Functional.

Requirement Statements can also be given a context by associating them with other documentation methods, such as Use Cases. This will be the topic of my next post.