Re: [Cdk-devel] SMARTS operator precedence..Help

[Nina J. <ni...@ac...>]

Hello,

& and ; both mean logical AND, and both translate to the same Java AND
operator. The difference is how the operands are grouped (precedence). Jiao is
absolutely right, the standard approach for any parsers to resolve operator
precedences is to use proper data structure (a tree or if I remember right a
stack could also do).

Examples:
1)
[!C;R]  (NOT aliphatic carbon ) AND in ring 
[!C&R]  NOT (aliphatic carbon AND in ring) 
2)
More
[C,N&H2]  means C OR (N AND H2]

[C,N;H2] means  (C OR N) AND H2


Hope this helps,
Nina


"sushil ronghe" <ron...@gm...> wrote:

> I mean how should i implement the matching in matcher class
> SMARTSOperatorAtom
> 
> 
> > The highest precedence expression should be left last to parse
> 
> 
> ok this is quite useful to me but my question was,
>  i want to know for matching what is the equivalent operator in java for &
> and ;
> suppose we have expression like this [C,N&H2] and [C,N;H2]
> what is the difference in between this two.
> 
> for both the operators this is true [C or N and H2]
> or something else.
> 
> 
> 
> 
> 
> 
> 
> On 4/20/07, Jiao, Dazhi <dj...@in...> wrote:
> >
> > Sushil,
> >
> > When parsing a language with binary operators, the TREE structure is the
> > key.
> >
> > To do precedence, please refer to my previous email about a
> > "LogicalOperator" class and my JJTree code.
> >
> > The BNF I created for parsing binary operators is:
> >
> > LogicalExpression ::= "[" AndOrExpression "]"
> > LowAndExpression ::= OrExpression ( ";" LowAndExpression )?
> > OrExpression ::= ExplicitHighAndExpression ( "," OrExpression ) ?
> > ExplicitHighAndExpression ::= ImplicitHighAndExpression ( "&"
> > ExplicitHighAndExpression )?
> > ImplicitHighAndExpression ::= NotExpression ( ImplicitHighAndExpression )
> > ?
> >
> > The highest precedence expression should be left last to parse. As you
> > can see, this basically will create a partial binary parse tree.
> >
> > Logical bonds are similar to this.
> >
> > I hope this helps. and I really suggest you to take a look at the BNF I
> > created. It's in the previous email and in the JJTree code. I made
> > a little changes to add ring identifiers. But the basic structure is the
> > same. Even if we decide on JavaCC instead of JJTree, a BNF is
> > always helpful to have a full picture of the language.
> >
> > David
> >
> > sushil ronghe wrote:
> > >
> > > As a smart parser has completed a significant part of smarts expression.
> > > i think this is the time to incorporate aromatic atom,and support for
> > > expressions
> > > like atom with hydrogenes.Ex :c:[nH1]  or [CH2] etc.. that will be
> > > done easily.
> > >
> > > But in operator precedence i am really unable to think how should one
> > > implement that.
> > > at present for both these operator "&"  and ";"  i have added the
> > > "*and"* operator see the file
> > > SMARTSOperatorAtom in "org.openscience.cdk.isomorphism.matchers.smarts".
> > >
> > > please help me to understand operator precedence.
> > >
> > > --
> > > ********************************
> > > sushil ronghe
> > > Center of Pharmacoinformatics
> > > India
> > > *********************************
> > > ------------------------------------------------------------------------
> > >
> > >
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