Prolog 执行查询
这直接来自在线教程,我得到了一个自上而下的设计错误,有帮助吗?
employee(193,'Jones','John','173 Elm St.','Hoboken','NJ',
12345,1,'25 Jun 93',25500).
employee(181,'Doe','Betty','11 Spring St.','Paterson','NJ',
12354,3,'12 May 91',28500).
employee(198,'Smith','Al','2 Ace Ave.','Paterson','NJ',
12354,3,'12 Sep 93',27000).
给定这些基本关系(也称为外延关系),我们可以使用 Prolog 过程定义来定义其他关系,以回答我们可能对数据产生的问题。例如,我们可以定义一个新关系,其中包含所有收入超过 28,000 美元的员工的姓名:
well_paid_emp(First,Last) :-
employee(_Num,Last,First,_Addr,_City,_St,_Zip,_Dept,_Date,Sal),
Sal > 28000.
This is directly from a tutorial online, and I get a top down level design error, help?
employee(193,'Jones','John','173 Elm St.','Hoboken','NJ',
12345,1,'25 Jun 93',25500).
employee(181,'Doe','Betty','11 Spring St.','Paterson','NJ',
12354,3,'12 May 91',28500).
employee(198,'Smith','Al','2 Ace Ave.','Paterson','NJ',
12354,3,'12 Sep 93',27000).
Given these basic relations (also called extensional relations), we can define other relations using Prolog procedure definitions to give us answers to questions we might have about the data. For example, we can define a new relation containing the names of all employees making more than $28,000:
well_paid_emp(First,Last) :-
employee(_Num,Last,First,_Addr,_City,_St,_Zip,_Dept,_Date,Sal),
Sal > 28000.
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可能您正在使用 Prolog 系统,该系统显示 well_paid_emp/2 的单例警告。
并非所有 Prolog 系统都允许 _作为单例,即在规则中仅出现一次的变量。
It could be that you are using a Prolog system which shows a singleton warning for well_paid_emp/2.
Not all Prolog systems allow _<Capital><Rest> as singletons, i.e. variables that occur only once in a rule.