Consider the following knowledgebase, where each line represents a separate fact

ID: 3833176 • Letter: C

Question

Consider the following knowledgebase, where each line represents a separate fact that is known to be true. Here, A, B, C, D, E are predicates, x, y are variables, and Greek letters alpha and beta are constant object identifiers. Forall x, A(x, alpha) B(x) Forall x, C(x) Lambda D(x) (exist y, A(y, x) Lambda B(y)) Forall x, A(x, alpha) A(x, beta) Forall x, C(x) E(x) D(x) exist x, A (x, beta) Lambda B(x) C(alpha) C(beta) Draw the resolution tree for answering the query exist x, C(x) Lambda E(x) ? Your answer should give the binding for x if such an x exists. Be sure to first convert the logical expressions (including the negated query) into canonical form (CNF) and then provide a resolution tree showing the variable bindings.

Explanation / Answer

The X++ keywords shown in the following table are reserved. These keywords cannot be used for any other purpose.

The asterisk (*) is also used in X++ SQL. One use is to signify all fields from the tables on a selectstatement. Another use is as a wildcard with the like operator, to signify 0 to many characters of any kind. The like operator also uses the ? character.

Also affects literal strings, by negating the effect of the escape character, and by enabling the string to span more than one line in the source code. The new line is represented by one character of hexadecimal 0x0A, which is commonly called a line feed. No carriage return character of hexadecimal 0x0D is included, as in 0x0D0A.

The colon (:) character is also used on the switch statement.

The question mark (?) character is also used by the like operator to signify exactly one character of any kind. The like operator also uses the * character.

A table can also be modified as abstract by setting its Abstract property to Yes in the AOT, or by using the DictTable class. The Abstract property defaults to No, and it cannot be set unless the table is extended by another table. Each row in an abstract table must have a dependent row in a derived table. This means that each row in an abstract table has a value greater than 0 (zero) in its InstanceRelationType property field. There are no other effects from marking a table as abstract.

Informally, programmers often use the term concrete to describe a class that is non-abstract.

Table Inheritance Overview

breakpoint;

X++, C# Comparison: Event

myDelegate += eventHandler(OtherClass::myStaticMethod);

X++, C# Comparison: Event

The firstOnly keyword does not guarantee that a maximum of one record is retrieved by an X++ SQL select statement. If the AOS can use the EntireTable cache to satisfy the data demands of the select statement, the firstOnly keyword is ignored.

Set-based Caching

YourTable ytBuffer; flush ytBuffer;

The string on the right side of the like operator must use four backslash characters to represent one backslash. Examples follow:

((12 mod 7) == 5) is true.

An explicit transaction completes at either ttsAbort or at the outermost ttsCommit.

For a stand-alone select statement, the transaction duration is the duration of the select command. However, the database sometimes enforces the equivalent of repeatableRead in individual select statements even without this keyword appearing in your X++ code (depending on how the database decides to scan the tables).

while select Statements

Reserved word Description More information ! Not. Relational Operators != Inequality operator (not equal to). Relational Operators # Prefix on macro names. How to: Use #define and #if to Test a Macro & Binary AND. Arithmetic Operators && Logical AND. Relational Operators ( Function call operator, which indicates the beginning of the function call. ) Function call operator, which indicates the end of the function call. * Multiply.

Arithmetic Operators ^ Binary XOR. Arithmetic Operators | Binary OR. Arithmetic Operators || Logical OR. Relational Operators ~ Not. Arithmetic Operators + Plus. Arithmetic Operators ++ Increment. Assignment Operators += Additive assignment. Assignment Operators , Comma operator. Expressions separated by commas are evaluated left-to-right. – Minus. Arithmetic Operators — Decrement operator. Assignment Operators -= Subtractive assignment. Assignment Operators . Class member access operator, for example, formRun.run accesses the run method of an object of the class type FormRun. / Divide. Arithmetic Operators Escape in strings. Escapes extra quotation marks, and certain letters such as for tab. @ Escape of keywords. For example, str @abstract; would fail to compile without the @ sign.

: Field declaration or label specifier.

The colon (:) character is also used on the switch statement.

:: Used to call static (class) methods: ClassName::methodName. ; Terminates statements. Used in for loops or as a separator of statements. < Less than. Relational Operators << Left shift. Arithmetic Operators <= Less than or equal. Arithmetic Operators = Assignment operator. The argument to the left of “=” is set to the value of the argument to the right. Assignment Operators == Returns true if both expressions are equal. Relational Operators > Greater than. Relational Operators >= Greater than or equal. Relational Operators >> Right shift. Arithmetic Operators ? Ternary operator.

The question mark (?) character is also used by the like operator to signify exactly one character of any kind. The like operator also uses the * character.

Ternary Operator (?) [ Array declarator, open. Must be used with “]“. ] Array declarator, close. Must be used with “[“. { Indicates the beginning of a number of statements. The last of these statements must be followed by a “}“. } Indicates the end of a number of statements. A “{” must appear before the first of these statements. abstract Class and method modifier. An abstract class cannot be constructed with the new keyword. An abstract method cannot be called.

Informally, programmers often use the term concrete to describe a class that is non-abstract.

Method Modifiers

Table Inheritance Overview

anytype The method can return any data type. Anytype as Needed when you assign a base class variable to a derived class variable. For example, given a Derived class that extends a Base class, the statement myDerived = myBase as Derived; avoids a compiler error by using the as keyword. This keyword also applies when you assign a base table variable to a derived table variable. Expression Operators: Is and As for Inheritance asc An option on the order by or group by clause in a select statement. The sorting is ascending. Select Statement Syntax at Specifies the position of a print window. Print Statements avg Returns the average of the fields from the rows specified by the group by clause in a selectstatement. Select Statement Syntax break Immediate exit from code block. Break Statements breakpoint Represents a breakpoint that is set for debugging purposes. To set a breakpoint in your code, write:

breakpoint;

by Part of a reserved term, such as group by and order by. byref Specifies that the parameter being passed to the called method is being passed by reference (address), instead of by value. Byref is used in X++ when calling a .NET method that takes a parameter by reference (such as with the C# keywords out or ref). How to: Use the byref Keyword for CLR Interop. case Selection within a switch statement. Switch Statements catch Used in exception handling. Exception Handling with try and catch Keywords changeCompany Changes database settings to another company. Change Company Design Pattern class Declares a class. Classes in X++ client Method modifier. Method Modifiers container Specifies a variable of type container. Containers continue Forces the next iteration of a loop. Continue Statements count Returns the number of records from the rows specified by the group by clause in a select statement. Select Statement Syntax crossCompany Causes a select statement to return data for all companies that the user is authorized to read from. Cross-Company X++ Code Basics date Specifies a variable of type date. Dates default Default case within switch statements. Switch Statements delegate A class member that is able to store multiple references to methods in other classes, and to call all those methods when prompted to do so. A delegate can store references to various kinds of methods including the following:

static methods on X++ classes
instance methods on X++ classes
methods on .NET Framework classes

Event Terminology and Keywords

X++, C# Comparison: Event

delete_from Allows you to delete multiple records from the database at the same time. delete_from desc An option on the order by or group by clause in a select statement. The sorting is descending. Select Statement Syntax display Method modifier. Method Modifiers div Integer division. Arithmetic Operators do Beginning of a do...while loop. Do…while Loops edit Method modifier. Method Modifiers else Conditional execution (if...else). if and if … else Statements eventHandler Must be used each time you either add or delete a method reference from a delegate by using the += or -= operator. For example:

myDelegate += eventHandler(OtherClass::myStaticMethod);

Event Terminology and Keywords

X++, C# Comparison: Event

exists Used with join clauses in select statements. Select Statement Syntax extends A class or interface declaration clause. If your class does not explicitly extend another class, your class is considered to extend the Object class (as if you had written “extends Object”). Creating a Subclass false Boolean literal. Booleans final Class and method modifier. Method Modifiers firstFast Used in select statements to speed up the fetch for the first row. Select Statement Syntax firstOnly Used in select statements to fetch only the first record.

Select Statement Syntax

Set-based Caching

firstOnly10 Same as firstOnly, except returns 10 rows instead of one. firstOnly100 Same as firstOnly, except returns 100 rows instead of one. firstOnly1000 Same as firstOnly, except returns 1000 rows instead of one. flush Clears an entire table cache. Here is the syntax for the flush statement:

YourTable ytBuffer; flush ytBuffer;

Set-based Caching for For loop iteration. For Loops forceLiterals Used in select statements to reveal actual values that are used in where clauses to the Microsoft SQL Server database at the time of optimization. Select Statement Syntax forceNestedLoop Forces the SQL Server database to use a nested-loop algorithm to process a particular SQL statement containing a join. Select Statement Syntax forcePlaceholders Used in select statements to instruct the kernel not to reveal the actual values used in where clauses to the Microsoft SQL Server database at the time of optimization. Select Statement Syntax forceSelectOrder Forces the SQL Server database to access the tables in a join in the specified order. Select Statement Syntax forUpdate Selects records exclusively for update. The operation to be performed on the records that are fetched is an update. Depending on the underlying database, the records may be locked for other users. Select Statement Syntax from Part of a select statement. The from clause specifies the table in which the columns exists. Select Statement Syntax group Part of the group by clause in a select statement. Select Statement Syntax if Conditional execution. if and if … else Statements implements Implements an interface. Interfaces Overview insert_recordset Copies data from one or more tables into one resulting destination table on a single server trip. insert_recordset int Specifies a variable of type integer (32-bit). Integers int64 Specifies a variable of type integer (64-bit). Integers interface Interface declaration. Interfaces Overview is Asks whether the object referenced by a class variable either inherits from the given class or is of the given class. For example, given a Derived class that extends a Base class, the expression (myDerived is Base) returns true. This keyword applies to class inheritance and table inheritance. Expression Operators: Is and As for Inheritance join Tables are joined on columns common to both tables. You can generate a single result set based on multiple tables through the use of joins. Select Statement Syntax like Tests for matches by pattern, with wildcard symbols * and ?.

The string on the right side of the like operator must use four backslash characters to represent one backslash. Examples follow:

(“\” like “*\*” ) //Resolves to false.
(“\” like “*\\*”) //Resolves to true.

Relational Operators maxof Returns the maximum of the fields from the rows specified by the group by clause. Select Statement Syntax minof Returns the minimum of the fields from the rows specified by the group by clause. Select Statement Syntax mod Returns the integer remainder of the left expression1 divided by the right expression2. Informally this is sometimes called the modulo operator.

((12 mod 7) == 5) is true.

new Operator. Creates an instance of an anonymous class that is assignment-compatible with the named class/interface reference variables, or allocates memory for an array. next Fetches the next record in a table. noFetch Indicates that no records are to be fetched at present. Select Statement Syntax notExists Used with join clauses in select statements. Select Statement Syntax null Symbolic constant. optimisticLock Forces a statement to run with optimistic concurrency control, even if a different value is set on the table. Select Statement Syntax order Part of the order by clause in a select statement. Select Statement Syntax outer outer join. Select Statement Syntax pause Halts the execution of a job. The user is asked to state whether execution should continue. Select Statements pessimisticLock Forces a statement to run with pessimistic concurrency control, even if a different value is set on the table. Select Statement Syntax print Allows you to display output on the screen. Print Statements private Method access modifier. Method Access Control protected Method access modifier. Method Access Control public Method access modifier. Method Access Control real Specifies a variable of type real. Reals repeatableRead Specifies that no other transactions can modify data that has been read by logic inside the current transaction, until after the current transaction completes.

An explicit transaction completes at either ttsAbort or at the outermost ttsCommit.

For more information, see the documentation for the underlying relational database product. retry Used in exception handling. Exception Handling with try and catch Keywords return Exits from a method. Declaration of Methods reverse Records are returned in reverse order. Select Statement Syntax select The select clause designates which columns or views are shown in the result set. Select Statements server Method modifier. Method Modifiers setting Used with the update_recordset command. update_recordset static Static methods may not refer to instance variables (only to static variables); may be invoked by using the class name rather than on an instance of the class (“MyClass.aStaticProcedure“). Method Modifiers str Specifies a variable of type string. Strings sum Returns the sum of the fields from the rows specified by the group by clause in a select statement. Select Statement Syntax super Calls the method that was overridden by the current method. Table Methods switch Switch selection statement. Switch Statements tableLock Obsolete; tableLock is no longer available. this A reference to the current instance of the class.
Used in X++ code inside a method of the class.
Used to reference method members of the class, but not field members of the class.public str getFullName() { // Next statement fails to compile without ‘this.’. return this.concatenateFirstAndLastNames(); } Loosely similar to the system variable that is named element. You use element in form control methods to reference the containing form. For more information, see Using Variables with Forms. throw Used in exception handling. Exception Handling with try and catch Keywords true Boolean literal. Booleans try Used in exception handling. Exception Handling with try and catch Keywords ttsAbort Discards all changes in the current transaction. Transaction Integrity ttsBegin Marks the beginning of a transaction. Transaction Integrity ttsCommit Marks the end of a transaction. Transaction Integrity update_recordset Allows the manipulation of row sets within one operation. update_recordset validTimeState Filters rows that are retrieved from a valid time state table by an X++ SQL select statement. For example: select validTimeState(myDateEffective) * from xMyTable; …or… select validTimeState(myDateFrom, myDateTo) * from xMyTable; Effects of Valid Time State Tables on Read and Write Operations void Identifies a method that does not return a value. Declaration of Methods where Part of a select statement. The where clause specifies the conditions to be satisfied; that is, the rows that you want to include in the result. Select Statement Syntax while Iteration statement. Executes a statement or block repeatedly when a test condition is true. While Loops

while select Statements

window Allows you to alter the size of the output window. Print Statements

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