Requirements Smells make SQL Smells!


Your SQL smells because your Requirements smell!
Your SQL smells because your Requirements smell!

Recently I read an article by Phil Factor on the subject of “SQL Smells”. Phil (apparently not his real name), identifies a number of “smells” which he thinks indicate that a database design or SQL code needs to be reviewed. He classifies some of these as “Problems with Database Design”. I would go further and say some of them are problems with database requirements! In other words, your SQL smells because your Requirements smell!

“Requirements Smells cause SQL smells!”

I no longer claim to be a “Developer” and I have never claimed to be a DBA (Database Administrator), though I have found myself in the position of being an “accidental DBA”. The thought that Requirements could smell bad concerned me.

This realisation made me think about problems with Requirements in general and problems with databases in particular. It is better to avoid a problem rather than cure it, so I’m writing a series of blog posts on how to recognise problems in Requirements and prevent them from becoming “SQL Smells”.

Database design and SQL smells

Any computer system contains a “model” of the world it works with. This model forms the foundations of the system. If the system does not contain a concept, then it cannot work with it!

A simplified database design process
A simplified database design process

When people start to create a system they have to decide what concepts their system needs. This is the “Conceptual Model”. This model is transformed through a “Logical Model” until it finally becomes the “Physical Model”, which is the design for the database. The Conceptual and Logical models are not just first-cut versions of the Physical Model, different design decisions and compromises are made at each stage.
This is nothing to do with “Waterfall”, “Agile” or anything to do with any specific development process. In fact, this approach is pretty universal, whether formally or not. Some people combine the different stages, but there are risks to doing that.

A simple way of looking at the Conceptual Model is to say that it is concerned with finding out:

  • What the business and system need: at the conceptual stage these are known as “Entities”
  • What we need to know about those things: these are the “Attributes” of the Entities
  • We also need to document “Business Rules”: some of these will be represented as “Relationships”.

During the design and development process:

  • Entities will tend to become table definitions
  • Attributes will become the columns within those tables
  • Business Rules may become so-called “constraints”.
Different Requirements become affect different aspects of the database
Different Requirements become affect different aspects of the database

A poor Conceptual Model or bad design decisions can lead to systems which are difficult to build, maintain and use, and which do not perform well either. Once again,

“Requirements Smells will cause SQL Smells”

The idea of “smells” can help us address potential problems earlier and more cheaply.

Where are these “Requirements smells”?

I’m going to group my bad smells in a slightly different way to Phil Factor. I primarily work as a Business Analyst, so I am going to concentrate on “smells” to look for at the Conceptual and Logical Stages of specifying the Requirements for a database, starting with the smell that Phil describes as “The God Object”!

Context Diagrams: Putting things in Context

Context Diagrams: Putting things in Context

Simple Context Diagram, application of Context Diagrams
Simple Context Diagram

Every Business Analyst should know something about Context Diagrams. I often draw an informal Context Diagram as the one of my first activities when I start a new project. Context Diagrams are good for focussing the mind and reminding you what you don’t know and need to find out.

What is a Context Diagram?

You have almost certainly seen Context Diagrams, even if you haven’t recognised them by name. A Context Diagram is a shape (usually a rectangle or circle) which represents “the system” which is the focus of our interest. This shape is surrounded by other shapes which represent things like:

  • Users of the system (or actors)
  • Other systems

The satellite shapes are joined to “the system” by lines. Sometimes the arrows on the lines have real significance, sometimes they are there for decoration.

Context Diagrams were commonly used as the top-most level in decomposition methods (such as SSADM). They are still with us in the form of the Use Case diagram in UML.

What will a Context Diagram tell us?

A Context Diagram will tell us about who uses the system we are looking at. It also tells us about the other systems it interacts with. The diagram actually tells us very little about our system!

When are Context Diagrams useful?

Context Diagrams are useful at towards the start of the project. They are good for communication and especially good for summarising who and what interacts with the system.

Although they don’t define our system at all well, they do make it clear what is outside. As a consequence, they are good for communicating “scope”. I even use them to help define scope during project initiation.

A really good use of Context Diagrams is to emphasis interfaces with other systems.

Limitations of Context Diagrams

There is something seductive about a well-drawn Context diagram. It seems to say a great deal, but actually it doesn’t say a lot.

It is wrong to try and make a Context Diagram do too much. Imagine a diagram with tries to show connections with 100 different objects. It would turn into a mess which nobody could read. As a result, the number of satellites is often edited. That makes the diagram easier to read but removes important information.

As a consequence, Context Diagrams are best used for illustration and communication, rather than definition.


Context Diagrams are a great way of providing overview and “putting things in context”! They are easy to produce and people understand them intuitively. They are good for communicating ideas to a non-technical audience.

To get the best from Context Diagrams you have to recognise their limitations. They are good at describing what is outside “the system” but they say very little about the system itself. They are not very good for detailed definition, and if they contain too much detail they actually become less useful!

Business Analysis: Pictures versus Words

Business Analysis: Pictures versus Words?

Image expressing "Pictures versus Words". An image of a pipe and the text "This is a pipe"
Pictures versus Words: This is a pipe

Business Analysts use models which are presented as pictures. Business Analysts also need to write text. This may give rise to a debate:

“Pictures versus Words – which is better?”

(In the picture I’m making a playful reference to Rene Magritte’s famous painting “The Treachery of Images”). Unfortunately, the honest answer to this question has to be “it depends”. It depends on what:

  • You trying to achieve with your model or text?
  • The business side wants and understands?
  • IT side needs and understands?
  • You comfortable with?

Inevitably the answer is going to finish up as a compromise.

The limitations of words

Words used as a bridge between Business and Information Technology
Words alone may form a weak bridge

Words are marvellous! You are reading this blog post! Informally, most projects start off with a short statement “we want to do something”. We add detail to that statement and it becomes a list of “requirements”. That is good, but as we start to describe our “pipe”, sometimes we find that “a picture (or model) really is worth a thousand words”.

In the “Pictures versus Words” debate, the strength of words is found when they are brief and used to define the details. They are less good for explaining how things relate to one-another.

Words alone may make for a weak bridge between business and IT. And beware! Lawyers have been arguing about the precise meanings of words since time immemorial!

The power of models (or pictures)

Orthographic projection sketch of a chair
Orthographic projection sketch of a chair

“Orthographic Projection” is one standard way of arranging different views of the same object. You know very quickly that the diagram describes a type of chair.

Picture models like engineering drawings are strong when they are used to provide overview and show how things relate to one another. By using different views of the same thing we can check each one against the others and detect inconsistencies at an early stage.


In summary, pictures and models are useful and so is text. Use both as appropriate. Add detail as you need it, but limit the amount of detail to what you need. Choose the models you use with care so that you can use them to validate the requirements. My advice is to apply Ward Cunningham’s comment “The simplest thing that could possibly work” to documentation and requirements.

Are you wearing a Business Analysis Hat?

Are you wearing a Business Analysis Hat?

Business Analysis Hat
Business Analysis Hat

Are you wearing a “Business Analysis Hat”? You may still find yourself performing Business Analyst activities even when it is not your job title.

For a great deal of my career my job title has been “Something… Analyst”.  I have found myself performing analyst activities even when “Analyst” has not been mentioned in the job description. Lots of people tell me they have had similar experiences.

Rigid demarcation or flexible roles?

Some organisations have rigid demarcation between roles. In these organisations just reading someone’s job title tells you what they do: Business Analyst, Project Manager, Developer etc.

In smaller, less structured organisations, everybody “mucks in” to do the work.

Even in the more rigid situation, Analysis is an activity overlaps with others. Analysis clarifies what needs to be done. Business Analysis is not so much a question of who is doing it, as what they are doing and what tools they are using. Anyone can find themselves wearing a Business Analysis Hat!

What kind of Business Analysis?

One of the classic metaphors used for Business Analysis is a bridge connecting “Business” and “Information Technology”.  Business Analysts use metaphor a lot. We spend a lot of time saying:

  • “This is a bit like that”, or
  • “This represents that”

When we do this we are trying to “facilitate” communication between the two sides of the bridge and helping each side understand what effect they are having on the other side. “Facilitate” is one of the buzz-words you may hear a lot!

Business Analysis Bridge
Business Analysis Bridge

This facilitation role has several aspects, which are not mutually exclusive. Some of the activities I have seen are:

  • Managing “Requirements” – Put what “The Business” asks for into a formal structure. These “Requirements” are used by “Information Technology”. “The Business” understands the solution in terms of these requirements.
  • Encapsulating IT – Summarise the complexity of “Information Technology” so “The Business” can make informed decisions.
  • Working with Numbers – Use IT tools to understand aspects of “The Business” and present those insights to the business.

What kind of tools will you use?

Analysts use “soft skills” and “documentation skills” but they also make extensive use of “models”. You will hear mention of:

  • Process Models
  • Data Models
  • Use Case Models
  • and several more.

Understanding what the different types of model can give you and choosing the appropriate model for you situation can make communication more effective. I plan to explain some of the different models and notations in later blog posts.


Business Analysis facilitates communication between The Business and Information Technology. Analysis clarifies what needs to be done. Almost anyone can find themselves “wearing the Business Analysis hat”!

Communication is not only in one direction. Analysis uses many kinds of model and using the model which is appropriate for the situation can make communication more effective.