Phrase Structure Rules

HPSG phrase structure rules are CFG based regenerative rules and thus can utilize the same CFG parsing algorithms. However, the terminal and non-terminal symbols used in CFG are not just symbols in HPSG but are AVM based signs, which contain syntactic and semantic information. There are some generalized rules and principles on phrase structures in HPSG, which restrict and control the formation of tree based on linguistic requirements such as agreement, transitivity, etc. Therefore, HPSG enforces control through feature structures and principles for well formed sentences.

In Head driven phrase structure grammar, as the name implies, one node in the phrase may act as the head node, which drives and controls the phrase. The head node may be any of the daughters in the phrase structure rule, know as ‘head daughter’. Urdu is predominantly a head final language. In HPSG based rules for Urdu, head daughter is usually the last daughter. As shown in (69), verb (V) is head of sentence, post-position (P) is head of post-positional phrase and case marker (C) is head of case phrase (KP). The head daughter node is marked with capital letter ‘H’.

(69) _{S NP H V}*

PP N H P →

→

The head daughter node is specified in order to satisfy agreement requirements of the phrase through Head Feature Principle or by co-indexing.

Head Feature Principle

The Head Feature Principle states:

(70) “In any headed phrase, the HEAD value of the mother and the HEAD value of the head daughter must be identical”.

(Sag, Wasow et al. 2004)

The HEAD feature takes value of type part-of-speech (pos), which contains AGR (agreement) feature. With the use of Head Feature Principle (HFP), the agreement requirements of head daughter are transferred to the mother. By expanding symbols in (69) to signs, we get rules as shown in (71). The head value of mother is the same as that of head daughter marked with letter ‘H’ by the use of HFP

(71)

*

HEAD HEAD HEAD

HEAD HEAD HEAD

⎡ ⎤ ⎡ ⎤ ⎡ ⎤ → ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤ → ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦ H H

phrase phrase word

verb noun verb phrase word word

pp noun pp

It is arguable in Urdu, if noun (N) and case marker (CM) make a case phrase (KP) such that CM is the head daughter as shown in (72) or these make a noun phrase (NP) such that noun is the head of phrase as shown in (73).

(72) KP N H CM word HEAD HEAD HEAD → ⎡ ⎤ ⎡ ⎤ ⎡ ⎤ → ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ ⎣ ⎦ ⎣ ⎦ H ⎣ ⎦ phrase word noun cm cm (73) NP H N CM

HEAD HEAD HEAD

→

⎡ ⎤ ⎡ ⎤ ⎡ ⎤

→

⎢ ⎥ ⎢ ⎥ ⎢ ⎥

⎣ ⎦ H ⎣ ⎦ ⎣ ⎦

phrase word word noun noun cm

It is later shown in Chapter 7, that HEAD of both noun and case marker impart feature to mother HEAD, and although noun be marked as head daughter, the agreement of noun is selected by case marker and the resultant mother must have head value as noun as shown in (73). Based on the above-described consideration a modification in the HFP for Urdu is being proposed as shown in (74).

(74) “In any headed phrase, the HEAD value of the mother and the HEAD value of the head daughter must be identical, unless specified otherwise”.

Valance Feature

The VAL (valance) feature is used to show that one grammatical category requires others for completion. Thus, transitivity requirements for the verbs, requirement of noun for adjectives, and determiner requirement for nouns are handled through the valance feature. The VAL feature contains two main features, the SPR (specifier) and COMPS (complements). In an English sentence, the specifier noun phrase of verb represents subject, while verb complements represent object requirements represented by verb transitivity. Since English is a SVO language, the verb splits subject and objects. In HPSG, the linear order is taken into account and if a noun phrase comes before a verb then it is taken as a subject, and other noun phrases which appear after verb are taken as objects and are also known as complements of verb in HPSG. The values of SPR and COMPS features are represented as lists so these can hold multiple values. A value or more in the valence list represents need of such an item for the completion, while empty list signals that there is no requirement for the completion.

(75) The Valance Principle

Unless the rule says otherwise, the mother’s values of the VAL features (SPR and COMPS) are identical to those of the head daughter.

(Sag, Wasow et al. 2004)

The following Head-Complement and Head-Specifier rules are exception to the valance principle. Therefore, if the complements and/or specifier are found, the valance requirements of mother are satisfied, otherwise, mother will inherit the same requirement from the daughter according to ‘the valance principle’.

Head Complement Rule

The head complement rule, in the form of regenerative rule, is shown in (76), which states that if a head daughter requires ‘n’ complements and all ‘n’ are identified as sisters to head daughter, then the complement requirements of the mother are satisfied.

(76) VAL SPR 1 n

VAL COMPS COMPS 1 , n,

⎡ ⎡ ⎤⎤ ⎡ ⎤ ⎢ ⎥ → ⎢ ⎥ ⎢ _{⎡ ⎤}⎥ ⎢ ⎢ ⎥⎥ ⎢ ⎣ ⎦⎥ ⎣ ⎦ ⎣ ⎣ ⎦⎦ H phrase " "

However, if any one or more of ‘n’ complements is not found as sister to head daughter, then according to the valance principle (75), that will appear in the list of mother node and the resultant mother phrase is incomplete until its complements list is not empty.

Head Specifier Rule

The head specifier rule requires that item(s) specified in the list of SPR feature must be identified as sister to head daughter to satisfy the requirement and, thus, completing the mother phrase.

(77) 1 VAL SPR 1 VAL SPR _COMPS ⎡ ⎡ ⎤⎤ ⎡ ⎤ ⎢ ⎥ → ⎢ ⎥ ⎢ _{⎡ ⎤}⎥ ⎢ ⎥ ⎢ ⎣ ⎦⎥ ⎢ ⎥ ⎣ ⎦ ⎣ ⎣ ⎦⎦ H phrase

The subject noun phrase acts as specifier for HEAD verb and determiner acts as specifier for HEAD noun. In Urdu, where phrase order of sentence daughter phrases is relatively free, SPR and COMPS features have no difference, but in order to keep the correspondence with English based HPSG, the SPR is used for subject and COMPS are used for objects and other noun phrases in Urdu.