2.3 PRODUCTIONS A number of differe

2.3 PRODUCTIONS
A number of different knowledge representation tec hniques have been devised. These include rules, semantic nets, frames, scripts, knowledge-representation languages such as KL-1 (Woods 83) and KRYPTON (Brachman 83), conceptual graphs (Sowa 84), and others (Brachman 83). As described in Chapter 1, production rules are commonly used as the knowledge base in expert systems because their advantages greatly outweigh their disadvantages.
One formal notation for defining productions is the Backus-Naur form (BNF ; McGettrick 80). This notation is a metalanguage for defining the syntax of a language. Sytax defines the form, whereas semantics refers to meaning. A metalanguage is a language for describing languages. The prefix meta means “above”, and so a metalanguage is “above” normal language.
There are many types of languages: natural languages, logiclanguages, mathematical languages. The BNF notation for a simple English language rule that a sentence consists of a noun and a verb followed by punctuation is the following production rule:
::=
Where the angle brackets, , and ::= are symbols of the metalanguage and nt of the language eing specified. The symbol “::=” means “is defined as” and is the BNF equivalent of the arrow,  used in Chapter 1 with production rules. In order to avoid confusion with the Pascal assignment operator, :=, we will use the arrow.
The terms within angel brackets are called nonterminal symbols or simply nonterminals.a nonterminal is a variable in that it represents another term. The other term may be either a nonterminal or a terminal. A terminal cannot be replace by anything else and so is a cnstant.
The nonterminal is special because it is the one start symbol from which the other symbols are defined. In the definition of programming languages, the start symbol is usually named . The production rule

States that a sentence is composed of a subject followed by a verb, followed by an end-mark. The following rules complete the nonterminals by specifying their possible terminals. The bar means “or” in the metalanguage.
 I | You | We
 left | came
 . | ? | !
All possible sentences in the language, the productions, can be produced by successively replacing each nonterminal by its right-hand-side nonterminals or terminals until all nonterminals are eliminated. The following are some productions:
I left.
I left?
I left!
You left.
You lef?
You left!
We left.
We left?
We left!
A set of terminals is called a string of the language. If the string can be derived from the start symbol by replacing nonterminals by their definition rules, then the string is called a valid sentence. For example “We”, “WeWe”, and “leftcamecame” are all valid string of the language, but are not valid sentences.
A grammar is a complete set of production rules that defines a language unambiguously. Although the previous rules do define a grammar, it is a very restricted one because there are so few possible productions. For example, a more elaborate grammar could also include direct object, as in the productions.

 home | work | school
Although this is a valid grammar, it is too simple for practical use. A more practical grammar is the following in which the end-mark has been left out for simplicity :


 < adjective>
 a | an | the | this | these | those
 man | eater
 is | was
 dessert | heavy
The is used to andicate a specific item. Using this grammar, sentences such as
The man was a dessert eater
An eater was the heavy man
Can be generated.
A parse tree or derivation tree is a graphic representation of a sentence decomposed into all the terminals and nonterminals used to derive the sentence. Figure 2.3 shos the parse tree for the sentence “the man was a heavy eater”. However, the string “man was a heavy eater” is not a valid sentence bacause it lacks the determiner in the subject phrase. A compiler creates a parse tree when it tries to determine whether statements in a program conform to the valid syntax of a language.
Sentence

Subject Phrase verb object Phrase

Determiner Noun determiner adjective noun


the man was a heavy eater

Figure 2.3 Parse Tree of a Sentence
The tree in Figure 2.3 shows that the sentence “the man was a heavy eater” can be derived from the start symbol by applying appropriate productions. The steps in this process are shown below; the double arrow, =>, means apply the productions shown.
=>

=>
=> the
=> man
=> was
=>
=> a
=> heavy
=> eater
An alternative way of using productions is to generate valid sentences by substituting all the appropiate terminals for nonterminals, as discussed previously. Of course, not all productions, such as “the man was the dessert”, will make much sense.

Hasil (Bahasa Indonesia) 1:

2.3 PRODUKSI Sejumlah pengetahuan berbeda representasi tec hniques telah dirancang. Ini termasuk aturan, jaring semantik, frame, script, pengetahuan-representasi bahasa seperti KL-1 (hutan 83) dan KRIPTON (Brachman 83), konseptual grafik (Sowa 84), dan lain-lain (Brachman 83). Seperti dijelaskan dalam Bab 1, aturan produksi biasanya digunakan sebagai basis pengetahuan dalam sistem ahli karena keuntungan mereka sangat lebih besar daripada kekurangan mereka. Satu formal notasi untuk mendefinisikan produksi adalah bentuk Arequipa-Naur (jurnal BNF; McGettrick 80). Notasi ini merupakan suatu metabahasa untuk mendefinisikan sintaksis bahasa. Sytax menentukan bentuk, sedangkan semantik mengacu pada makna. Metabahasa adalah bahasa untuk menggambarkan bahasa. Awalan meta berarti "di atas", dan begitu metabahasa adalah "di atas" bahasa normal. Ada banyak jenis bahasa: bahasa alam, logiclanguages, bahasa matematika. Notasi jurnal BNF untuk bahasa Inggris sederhana aturan bahwa kalimat yang terdiri dari kata benda dan kata kerja diikuti tanda baca adalah aturan produksi berikut: ::= Mana kurung sudut, <>, dan:: = adalah simbol-simbol metabahasa dan PB eing bahasa yang ditentukan. Simbol ":: =" berarti "didefinisikan sebagai" dan jurnal BNF setara dengan Panah,  yang digunakan dalam Bab 1 dengan aturan produksi. Untuk menghindari kebingungan dengan operator penetapan Pascal,: =, kita akan menggunakan panah. Persyaratan dalam kurung malaikat disebut simbol nonterminal atau hanya nonterminals.a nonterminal adalah variabel yang diwakilinya istilah lain. Istilah yang lain mungkin nonterminal atau terminal. Terminal tidak dapat menggantikan lain dan sehingga cnstant. Nonterminal khusus karena merupakan simbol satu mulai dari mana simbol-simbol lainnya yang ditetapkan. Dalam definisi bahasa pemrograman, simbol mulai biasanya diberi . Aturan produksi  Menyatakan bahwa kalimat terdiri dari subjek yang diikuti oleh kata kerja, diikuti dengan tanda akhir. Aturan berikut lengkap nonterminals dengan menentukan terminal mereka mungkin. Bar berarti "atau" di metabahasa.  SAYA | Anda | Kami  meninggalkan | datang . | ? | ! Semua mungkin kalimat dalam bahasa, produksi, dapat diproduksi oleh berturut-turut menggantikan setiap nonterminal yang nonterminals right hand sisi atau Terminal sampai semua nonterminals dihilangkan. Berikut ini adalah beberapa produksi: Aku meninggalkan. Aku meninggalkan?Aku meninggalkan!Anda pergi.Lef Anda?Anda pergi!Kami meninggalkan.Kami meninggalkan?Kami meninggalkan!Seperangkat terminal disebut string bahasa. Jika string bisa berasal dari simbol mulai dengan mengganti nonterminals oleh aturan definisi mereka, maka string disebut kalimat yanga valid. Misalnya "Kami", "WeWe", dan "leftcamecame" adalah semua berlaku string bahasa, tetapi tidak kalimat-kalimat yang berlaku.Tata bahasa adalah satu set lengkap produksi aturan yang mendefinisikan bahasa yang jelas. Meskipun aturan sebelumnya menentukan tata bahasa, itu adalah sangat dibatasi karena ada begitu sedikit kemungkinan produksi. Misalnya, tata bahasa yang lebih rumit juga dapat mencakup obyek langsung, seperti dalam produksi. 
 home | work | school
Although this is a valid grammar, it is too simple for practical use. A more practical grammar is the following in which the end-mark has been left out for simplicity :


 < adjective>
 a | an | the | this | these | those
 man | eater
 is | was
 dessert | heavy
The is used to andicate a specific item. Using this grammar, sentences such as
The man was a dessert eater
An eater was the heavy man
Can be generated.
A parse tree or derivation tree is a graphic representation of a sentence decomposed into all the terminals and nonterminals used to derive the sentence. Figure 2.3 shos the parse tree for the sentence “the man was a heavy eater”. However, the string “man was a heavy eater” is not a valid sentence bacause it lacks the determiner in the subject phrase. A compiler creates a parse tree when it tries to determine whether statements in a program conform to the valid syntax of a language.
Sentence

Subject Phrase verb object Phrase

Determiner Noun determiner adjective noun


the man was a heavy eater

Figure 2.3 Parse Tree of a Sentence
The tree in Figure 2.3 shows that the sentence “the man was a heavy eater” can be derived from the start symbol by applying appropriate productions. The steps in this process are shown below; the double arrow, =>, means apply the productions shown.
=>

=> <.noun>
=> the
=> man
=> was
=>
=> a
=> heavy
=> eater
An alternative way of using productions is to generate valid sentences by substituting all the appropiate terminals for nonterminals, as discussed previously. Of course, not all productions, such as “the man was the dessert”, will make much sense.