To illustrate the different generation techniques, which I discuss in the following sections, I will first define a simple, but in some respects typical, grammar for a small subset of Dutch.
I assume in this grammar that all strings are built using a difference-list implementation of concatenation as in concatenative formalisms. Therefore, each binary rule extends the following:
To make the rules somewhat easier to read, I will not explicitly mention these constraints in the rules -- however for each rule they are present.
Lexical entries will generally specify their phonology as follows, where the variable Word is instantiated by some constant representing the terminal symbol associated with that lexical entry:
Note though that none of the conclusions of this chapter in any way depends on the restriction to assume such a concatenative base. In the next chapter I discuss other ways to combine strings -- the generation algorithms discussed here are all capable of handling such more powerful rules. In fact, some of the problems I will encounter for generation, can be solved in grammars in which concatenation is not the sole operation to construct phonological structures.
The value of the subcat feature (the label sc) is a list of signs. In this rule, the first element of the subcat list of the second daughter of the rule, is equated with the first daughter of the rule. The `remaining' elements on the list, i.e. the tail of the list is `percolated' to the mother node of the rule. If a verb selects several arguments then this vp rule can be applied iteratively. The following example clarifies this technique. Assume that some verb subcategorizes for four elements, called a, b, c and d. Then the parse tree for the saturated verb phrase dominating this verb, looks as in figure 3.1. The elements of this list are selected by a binary verb-phrase rule, one at the time. If selection is to the left, then the order of the elements on the list mirrors the order of the elements found in the string.Thus, the elements of the subcat list are selected one at the time. Note that in the case where elements are selected to the left of the head, the order of the elements on the subcat list is the reverse of the order of the actual elements in the string. Furthermore note that if a sign is saturated, then its subcat list is empty.
Furthermore, it is stated in this rule, that the semantics of the second daughter is identical with the semantics of the mother of the node. In the current grammar, semantic structures will invariably be built lexically; these structures are always unified between the semantic-head and the mother of a rule. Thus, the semantic-head, or `functor', of a rule is that daughter, which shares its semantics with the semantics of the mother node of the rule. This daughter not necessarily is the `syntactic-head' of the phrase. For example, modifiers often are analyzed as the semantic-head of the construction they modify, whereas the modified part of the construction is the syntactic head.
The semantics of a lexical entry is defined by sharings with the semantics of the elements it subcategorizes for. Some verbs are defined as in rule 2. In these entries it should be noted how semantic structures are defined by sharings with parts of the elements on the subcat list. Therefore, if such verbs are selected by the VP rule above, the semantics is gradually instantiated, when the arguments are selected. Note that this mechanism is essentially the mechanism assumed in UCG ; see also , and  for discussion.
In Dutch, the finite verb occupies the second position of a main clause, whereas in subordinate clauses it occupies the final position. Thus we have:
In order to be able to use the same verb phrase rules in both subordinate and main clauses, I will define a threading implementation of a `movement' analysis of verb second. This analysis uses the features v2 and lex, already mentioned in the foregoing rule 1. I assume that in main clauses the finite verb also occupies the final position, but in a phonologically empty way. Furthermore the information of this empty verb is then percolated through the v2 feature to the pre-VP position. The basic idea of this analysis is illustrated in figure 3.2. The information of the initial finite verb is percolated downwards to a phonologically empty verb, in the position of the finite verb in subordinate sentences.
In this rule the binary feature lex is used to implement the fact that only verbs, and not verb phrases, can be fronted to the verb-second position. The information of the verb in verb second position is percolated through the v2 feature. Furthermore, there is the option that a verb in Dutch can be `empty', in case the features in its `incoming' v2 feature unify with its own features, cf. rule 6.
In case a verb phrase should not dominate this empty verb, the grammar instantiates the v2 feature with some constant, for example the value . The grammar rule in rule 7 defines that a complementizer phrase consists of a complementizer and the argument for which this complementizer subcategorizes.
Such a complementizer `omdat' (the Dutch equivalent of `because') is defined in rule 8, where it should be noted that this complementizer requires that the verb phrase should not dominate the empty verb, by specifying the value of the v2 attribute. Furthermore note that the complementizer requires that the embedded verb phrase should be `saturated', i.e. should have selected its arguments, because it requires that the value of the sc attribute of the verb phrase for which it subcategorizes, is the empty list. This is a way to implement LFG's completeness requirement  on subcategorization specifications. In general, lexical entries require that the subcat lists of their arguments are empty.
Note that the position of this adverbial is usually analyzed as the topic position. The current simplification is motivated, because for the expository purposes of the grammar, it is not necessary to implement a gap-threading analysis of topicalization.
The grammar also allows some simple modification of verb phrases. Verb phrases may consist of an adverbial phrase followed by a verb phrase. The subcat list of the verb phrases is percolated, because in Dutch, unlike in English, adverbials can be interspersed with the arguments of the verbs:
Note that such sentences motivate the use of the binary verb phrase rule 1, giving rise to branching verb phrases, rather than flat verb phrases as in HPSG. Rule 11 defines that a verb-phrase may consist of an adverbial and a verb phrase.
Such an adverbial might for example be defined such as the following entry of `vandaag' (today) in rule 12.
We will not be very much interested in noun phrases; therefore I simply assume some noun phrases that are defined as in the following example for `Arie', `een dutje' (`a nap') and `leugens' (`lies'):
This second noun phrase will be used to construct the idiomatic verb phrase `een dutje doen' which means `to take a nap'.
A suitable parser for this simple grammar returns for the call
the following constraint on X0:
The resulting grammar is given in the figures 3.3, 3.4 and 3.5. Note that I left out the relation symbols `sign' for short.