2010
6
27
ةيزيلجنلاا ةغللا :ةبعشلا

a.
Symbol and referent
A symbol is something which we use to represent another thing - it might be a picture, a letter, a spoken or written word - anything we use conventionally for the purpose. The thing that the symbol identifies is the referent. This may sometimes be an object in the physical world (the word Rover is the symbol; a real dog is the referent). But it may be something which is not at all, or not obviously, present - like freedom, unicorns or Hamlet.
In studying the lexicon of English (or any language) we may group together lexemes which inter-relate, in the sense that we need them to define or describe each other. For example we can see how such lexemes as cat, feline, moggy, puss, kitten, tom, queen and miaow occupy the same semantic field. We can also see that some lexemes will occupy many fields: noise will appear in semantic fields for acoustics, pain or discomfort and electronics (noise = “interference”). Although such fields are not clear-cut and coherent, they are akin to the kind of groupings children make for themselves in learning a language. An entertaining way to see how we organize the lexicon for ourselves is to play wordassociation games.
There are several equivalent representations of sentence structure. Some of these are based on the constituent theory of sentence structure and the notion of phrase-structure grammar. These representations include models like phrase structure rules, tree diagrams, transition networks and box diagrams. Phrase-structure grammar uses for a sentence like “Nice dogs like cats” structure representation like the following:
S → NP VP
NP → A N

NP → N
VP → V NP
N → dogs
N → cats
V → like
A → nice
The derivation begins by replacing S with the symbols NP and VP by applying the rule S → NP VP. Each of the resulting symbols, namely NP and VP, can then be rewritten by applying the rules NP → A N and VP
→ V NP. This rewriting or replacement process continues until the string of words forming the sentence is produced.
This analysis can also be represented syntactically in different ways as:
1.
Tree Diagram
The operation of applying rules here consists of tree substitution The substitution procedure continues as long as there are branches that end in nodes labeled with symbols and it stops when all the branches end in leaves consisting of those words comprising the sentence. A tree constructed in the course of producing the sentence 'nice dogs like cats' is shown in the figure
2.
Transition Network
A tree diagram representation of the structure of a sentence is also equivalent to the Transition Network diagram representation. Such diagrams consist of a collection of arcs, the curved line segments in this case with an arrow head to indicate a direction. The arcs join nodes which

correspond to the beginning and end of the sentence, and to the spaces between the words. The nodes are usually identified with numbers that serve to keep track of the progress of the analysis of the sentence as follows:
3.
Box Diagram
Another sentence structure representation that is not normally displayed by a parser, but which is equivalent to the other representations discussed above is the box diagram.
As the accompanying figure illustrates, a box diagram consists of a collection of nested rectangles, each of which is identified by a category label. The following is a box diagram of the same sentence “Nice dogs like cats”
The three types of syntactic representations (tree diagrams, transition network and box diagrams) are all equivalent to the phrase structure rules deriving the same string of words producing the sentence “Nice dogs like cats”

Ambiguity occurs when a language element has more than one meaning. If the ambiguity is in a single word it is lexical ambiguity. If in a sentence or clause, it is grammatical or structural ambiguity.
We can illustrate lexical ambiguity with an example from Sue Townsend's
Secret Diary of Adrian Mole. Adrian displays a notice in school, advertising a gay society. When a teacher rebukes him, Adrian asks what is wrong with a club for people who want to be jolly or happy. Another example of lexical ambiguity is found in the sentence “I have seen them by the bank” when it is intentionally not clear whether the word bank refers to a bank of a river or a bank that we go to for money.
Structural ambiguity can often be seen in punning headlines, like the wartime example CHURCHILL FLIES BACK TO FRONT. The late polar explorer, Dr.
Vivian Fuchs, was the subject of a similar headline: DR. FUCHS OFF TO
ANTARCTIC. In this case, the structural ambiguity is not present to a reader who knows standard spelling, but might confuse a hearer, if the headline is spoken aloud. The absence of linking grammatical words (articles, conjunctions, prepositions) in headlines makes such ambiguity likely.
Other examples of structural ambiguity can be found in sentences like: a.
Visiting relatives can be annoying. b.
The lamb is too hot to eat.
The two examples should be explained to reveal the ambiguity. The lamb example can also be explained to combine both lexical and structural ambiguity