the shared experience of many people, to provide best-practice solutions to all employees.
Mykonos also provides business rules for other circumstances—circumstances that do not involve payments. There are business rules to protect the health of the Mykonos restaurant customers and to ensure that the local health codes are satisfied. There are business rules around safety, to ensure that no employees are hurt, especially since the restaurant business involves both fire and knives.
There are business rules around staffing and scheduling employees, to promote both fairness and efficiency and to reduce employee dissatisfaction. There are business rules about seating customers at tables and managing customers that are waiting to be seated. And even though menu design for a restaurant is largely left to the discretion of the restaurant head chef, there are some business rules about menu design—for example, to ensure that vegetarian customers always have at least two entrees from which to choose.
wine is served? Charging for Orders is silent on that situation; presumably other business rules apply. Similarly, if a glass of pinot noir is served to Joe’s party but neither Joe nor anyone else ordered it, Charging for Orders does not say whether it must be charged.
Business rules travel in groups. It is rare for a single business rule to exist by itself, without 5 or 20 others that apply to related situations. There are many other Mykonos business rules about payments. For example:
Splitting Bills: It is permitted that a server may split a bill only if the party agrees to bill splitting and the bill is split equally.
TheSplitting Billsbusiness rule provides guidance about bill splitting—the con- ditions under which it is permissible for customers to split a bill. There are two conditions that must be true if a bill is to be split. If the party does not agree to split the bill, the bill may not be split. And the bill may not be split if it is to be split 60-40 or anything other than equally.
Splitting Billsseems quite understandable, but only because we are relying on our existing knowledge about servers, parties, and restaurant bills—knowl- edge that we all have gained from eating in restaurants. Someone who has never eaten in a restaurant might wonder what these words really mean. If a person eats by himself, is that a party? What about 11 people who eat at two separate tables because there is no room to seat them all together? What is a bill, really? A com- plete business rule model that includes Splitting Bills needs to define some nouns: server, party, and bill. Charging for Orders also uses two nouns that need definitions: party and item. Is a glass of pinot noir an item? Is a cigar?
A shoe?
There are some other mysteries aboutCharging for Orders and Splitting Bills—mysteries at least to our fictional person who has never enjoyed a restau- rant meal. What does it mean for a party to incur a bill? Can a server incur a bill?
Can a bill incur another bill? What does bill splitting mean? What does it mean for a bill to be split equally? A complete business rule model needs to define verbs like incur and concepts like equal splitting. Later in this chapter, we show how all these terms are defined as part of a business rule model.
Why No Diagrams?
You might have noticed that the business rulesCharging for OrdersandSplitting Billsare shown here as sentences in English, not as diagrams. The business motiva- tion models in Chapter 3 were diagrams, as were the business organization models in Chapter 4 and the business process models in Chapter 5. Why are business rules textual when the models in the other three disciplines are graphical?
In fact, a business motivation model can be described in text instead of in a diagram. Consider the simple motivation model shown in Figure 6.1 (and
originally presented as Figure 3.5).Figure 6.1 can be expressed textually instead of visually:
The organization unitNoladefines the goalEstablish Regular Customers.
Nola establishes a strategy Offer Seasonal Menu that channels efforts towardEstablish Regular Customers.Nolaalso establishes a tacticOffer Discount Coupon that channels efforts toward Establish Regular Customers.
The text is equivalent to the diagram; from either you could create the other.
In reviewing a business motivation model with a subject matter expert, it is often convenient to show him the diagram and walk him through it by saying the equiv- alent text so that he understands each element in the diagram. Diagrams are (usu- ally) easier and faster for people to understand, so business motivation models are usually expressed graphically.
Business organizational models can also be expressed textually, in much the same way. So can business process models. Every model in this book can be expressed in English1instead of in lines and boxes and other graphical elements.
As with business motivation models, the usual practice is to express organization and process models graphically; as you’ve seen the resultant diagrams are easier and faster to understand than the equivalent words.
Business rules are different. Some experts have proposed graphical languages for business rules (e.g., Terry Halpin’s work [Halpin 2001]), but most people find the
1Of course, when we say English, we really mean any natural language: Japanese, Portuguese, Hindi, or any other of the world’s 7,000 written tongues.
Offer Seasonal Menus: strategy
channels efforts toward
Nola:
organization unit Establish Regular Customers: goal
defines
Offer Discount Coupon: tactic channels
efforts toward
establishes establishes
FIGURE 6.1 A simple motivation model
142 CHAPTER 6 Business Rule Models
words easier to understand than the diagrams. In our experience, a business profes- sional will more quickly understand a well-written business rule than she will under- stand a business process of equivalent complexity. Why? The reason is not clear.
Perhaps our brains are just wired to comprehend rules. Perhaps in our ancestral past there were advantages to quickly learning tribal rules articulated by a tribal elder, and advantages to quickly recognizing when a rule was violated. Presumably the East African savannah offered no such advantages to the quick learning of business processes.
Even though business rules are in practice written as sentences instead of diagrams, they are still business models. Not all models are visual. With business rules, the model is expressed in the logic of the text rather than in a diagram.
A business rule is a model because it fits the definition we introduced in Chap- ter 1: it is a simple representation of a complex reality. For example, theSplitting Billsrule we examined earlier is simple guidance that applies to thousands of dif- ferent restaurant situations, many of which are complex.
But there are some diagrams in this chapter. Although the business rules we examine are all shown as text, we do show diagrams of how those rules relate to other model elements, just as we showed diagrams in Chapter 5 of how activ- ities relate to goals and to objectives. We also include some simple diagrams that show how rules are constructed, that show the components of a rule and the ordering of those components. And we include fact type diagrams. As we explain later in the chapter, fact types are verbs used in rules and the nouns those verbs tie together. Fact types lend themselves to diagrams. So although there are no diagrams of business rules themselves, this chapter has many diagrams for other purposes.