Documentation

Defaults and Exceptions

Laws are typically drafted in a style where the rules that apply most generally are stated first, and more specific variations are stated later. Blawx calls this style "defaults and exceptions," and gives you a number of tools you can use to be able to encode defaults and exceptions without needing to modify multiple sections of code when a new exception is created.

Defaults and Exceptions in Blawx

The basic system of dealing with defaults and exceptions in Blawx can be described by these steps:

  • You indicate which sections of law led to which conclusions.
  • You can indicate which conclusions contradict one another.
  • You can indicate which sections overrule which other sections.
  • You can ask which conclusions are not overruled.

Blawx provides one block for each of these four capabilities, plus blocks that allow you to specify sections of the law.

According To

You indicate that a section of law reached a conclusion by using the "according to" block in the conclusion of your rule, indicating the section that reached the conclusion, and then including the conclusion statement as per usual. A rule with an "according to" conclusion looks like this:

According To Rule

Pre-Built "According To" Rule Block

Most of the time, you will be encoding a conclusion that is reached by the current section, so to save you time, Blawx adds a pre-loaded rule block in the Primary drawer that has the according to block and the current section selector block pre-loaded. The pre-loaded according to rule looks like this:

Preloaded According To Rule

According To Must be Used With According To or Holds

If you want to be able to use the holds block when running a query, the conclusion must be inside an according to block. You might want to use the holds block in order to be able to check whether or not a conclusion was overruled by another conclusion. However, you may just want to include details on the section of law that led to that conclusion in your explanations. (This use is discussed below in the section on the holds block.) In both cases, the according to block must be used with your conclusion.

Asking if Rules Reached a Conclusion

If you want to use a conclusion wrapped in an according to block as a condition in a different rule, you must use either the according to block or the holds block in that condition. Effectively, the conclusion "socrates is mortal" and "according to MA 1 socrates is mortal" are treated by Blawx as two unrelated statements.

Asking If Any Rule Reached a Conclusion

If you have multiple rules that reach the same conclusion, and all of these rules use the according to block; and if you want to use that conclusion in the conditions of another rule but you are not interested in where the conclusion came from, you can ask whether any section reached that conclusion by using an according to block and using the "any" variable block in place of the section selector. This method can also be used in a question, if what you are interested in knowing is whether that conclusion was reached by any section, regardless of which. That question would look like this:

According to Any Question

Asking Which Rules Reached a Conclusion

If you would like to find out which sections of your law reached a certain conclusion, you can find out by using a named variable in the according to block. This will typically only be useful in a question, and not in the conditions of a rule, because there is not currently a way to generate or use section values other than by using the section selector block, and displaying them in answers. A question asking "which sections concluded that socrates is mortal" could be posed like this:

According to Which Question

Opposes

When you make a query with the holds block, Blawx will only look to see if a conclusion has been overruled by another conclusion when those two conclusions "oppose" one another. The opposes block looks like this:

Opposes Block

By default, there are two types of statements that automatically oppose one another, without you needing to use an opposes block to say so:

  • If you have a statement, and the same statement wrapped in a "known false" block, those conclusions are automatically opposed.
  • If you have an attribute that has the "true / false" type, a statement that the value of that attribute is "true" for a given object, and a statement that the value of that attribute is "false" for the same object, are automatically opposed.

These two cover a majority of the types of opposition that you will usually want to use. The purpose of the opposes block is to allow you to be explicit about statements that oppose one another that Blawx cannot infer.

An Example Opposition

Consider, for example, that you are modeling rules about pet owners, and in these rules pet owners are deemed either "cat lovers" or "dog lovers", and that they are mutually exclusive. You might have a general rule that a person is a dog lover if they own a dog, and an exception that states a person is a cat lover if they own more cats than dogs.

To give effect to those rules, your default rule would conclude, using "according to", that the person was in the category dog lover. The exception rule would conclude, using "according to", that the person was in the category cat lover. Somewhere in your code you would need to specify that the statment "X is in the category cat lover" and the statement "X is in the category dog lover" are opposed, using an opposes block. Your opposes block might look like this:

Dog and Cat Opposed

Opposition is not Inconsistency

If you make two statements opposing using the opposes block, that applies only to the context of when you query whether either conclusion "holds". Blawx will not impose a general prohibition against concluding both things at the same time.

If you want to make two statements incompatible with one another, so that Blawx will never find an answer set that includes both statements, and regardless of whether the defaults and exceptions system is used, that is accomplished using the logical constraints block.

Likewise, Blawx knows that certain statements are inconsistent with one another, and will not allow both statements to be in the same explanation. For example, no explanation will include both the statement "socrates is mortal" and the statement "it is known false that socrates is mortal". If you use "according to" blocks to reach those conclusions, it is necessary for Blawx to be able to consider how these conclusions might both be found at the same time, and how the conflict might be resolved by your rules. So "according to section 1, socrates is mortal" and "according to section 1, it is known false that socrates is mortal" are not inconsistent, even if they come from the same rule.

Overrules

When calculating which conclusions "hold", Blawx first finds opposing conclusions that are reached by sections of your rules, and then sees whether one of your sections overrules the other. Providing Blawx with these overruling relationships is done with the Overrules block, which looks like this:

Filled Overrule Block

Dealing with Multiple Conclusions Per Section

Overrules are specified as one section overruling another section, and are not specific about which conclusion from that section is overruled. If you have sections that reach multiple conclusions, and the overrule relationships are different by conclusion, you will need to divide that section of your law into multiple sub-sections using the span feature of the CLEAN syntax. That will allow you to get a one-to-one relationship between sections and conclusions, so that your overrules block can be specific about what is and is not overruled in each case.

If your default reaches multiple conclusions, and your exception reaches multiple opposing conclusions, and the overruling relationship is the same for all of the pairs of conclusions, then a single overrule block will work fine. It is only necessary to break up your sections if there are multiple conclusions and if the overruling relationships are different between pairs of opposing conclusions. That also means that if you have a default that reaches 2 conclusions, and an exception that reaches 3 conclusions, 2 of which oppose the 2 conclusions in the default, you can use a single overrule block. An extra conclusion with no opposite will not affect how the overrule operates.

Deciding Where to Put the Overrules Block

Laws use a large number of different terminology to describe defeating relationships. Consider that a law might say "the default applies", and then say "despite the default, the exception applies." Here, the relationship between the two rules (exception overrules default) is specified in the exception. This can be called a "despite-style" overrule statement.

A law might also say "subject to exceptions, the default applies", and then say "the exception applies". The same overrule relationship (exception overrules default) is specified, but this time it is expressed in the default. This is a "subject-to-style" overrule statement.

Both of these styles are used regularly in legislative drafting, and the overrules block allows you to describe this relationship in your code wherever it appears in your law. If you are implementing a "despite-style" overrule statement, the overrule block goes in the code for the exception, and states "this section overrules other section". If you are implementing a "subject-to-style" overrule, the overrule block goes in your default rule, and states "other section overrules this section".

This flexibility about where the overrule statements are placed gives you the ability to keep your code organized the same way your laws is organized, which makes your code easier to write, verify, and maintain.

Conditional Overrules Blocks

Sometimes, there are complicated, conditional overrule statements set out in legislation. For example, consider a rule that says "this exception overrules the default for events occurring prior to date".

Because overrules blocks are statements, then can be used as the conclusions of rules. This makes it possible to create a rule that will conditionally determine whether an overrule statement applies, depending on facts like whether an event is prior to a date.

Note that the conclusion that the overrule exists can only be true or false in a given explanation. If you need the overrule to be active for some aspects of an explanation and not for others, such as when a rule states "this exception applies for the purposes of calculating salary in this section", you may not be able to get that effect by making a conditional overrule statement.

Holds

Once you have rules that set out which sections reach which conclusions using the according to block, describe any unusual oppositions using the opposes block, and set out which sections should prevail using the overrules block, you are now ready to ask whether a conclusion legally "holds". An example question looks like this:

Holds Question

This is done using the "holds" block in a question or condition, and then putting the conclusion inside the holds block. In order to save you time, the Primary drawer of the toolbox includes a question block with the "holds" block added for you.

Pre-Loaded Holds Question

The Meaning of Holds

In the current version of Blawx, "holds" has a very simple definition.

A conclusion holds if:

  • it was concluded, according to a section, and
  • it is not defeated.

A conclusion is defeated if:

  • it was concluded by an original section,
  • an opposing conclusion was concluded by another section, and
  • the other section overrules the original section.

Complicated Overruling Relationships

We have plans to expand the definition of "holds" in future version of Blawx to be able to deal with more complicated scenarios, but for now, the definition above is all that Blawx uses. One important shortcoming to note is that Blawx does not currently check to see whether the defeating section is itself defeated. As a result, if C defeats B, and B defeats A, and all three are concluded, C will hold as would be expected, and A will hold, which is likely not what your legislation meant.

To get around this in the meantime, it would be necessary to say explicitly in your code that C opposes A, and C overrules A.

Using Holds for Better Explanations

If you use "according to" to describe your rules, and you use "holds" in your question, your explanations will have access to information about the sections of your law by which those conclusions were reached.

For example, if you have a rule that says "humans are mortal", and a test that says "socrates is human" and asks "who is mortal", your explanation will read "socrates is mortal because socrates is human".

Explanation Without Holds

If, instead, you encode "according to section 1, humans are mortal", and in the question you ask "does it hold that anyone is mortal", your explanation will read "according to section 1 socrates is mortal because socrates is human." Also, the words "section 1" in the explanation will be highlighted, and when you hover over them you will have access to the text of the source rule.

Explanation With Holds

Currently, the defaults and exceptions system is the only way to get access to legislative text in your conclusions, so it can be a good idea to use the "according to" blocks and "holds" blocks in your code for that reason alone, even if you have no use for "overrules" or "opposes".

Making Implicit Overrules Explicit

An important thing to remember about how Blawx deals with defaults and exceptions is that it requires you to be explicit about which conclusions oppose one another, and which sections of the law overrule which other sections of the law.

In legislation, this relationship may not always be explicit. It may arise from a difference in the age of two rules, the jurisdiction of two rules, or the author of two rules. If your rules include these sorts of implicit overruling relationships, those relationships will need to be made explicit in your code.

Future Work: Choosing Sections

Currently, the only way to select sections for use in an overrule statement is using the section selector. If one rule is "despite section 1 subsections (1), (2), and (3)", the code for that rule will require three overrule statements. We have plans to add features to allow you to select sections and their subsections at the same time (scope selectors). We also want to allow entire rules to be organized hierarchically with regard to one another, so that you can easily encode and overrule by "any rule in a regulation made under this Act." Those features have not yet been implemented.