Fundamental Visual Prolog - the Data Layer - Revision history

Thomas Linder Puls: code update

2022-02-03T14:53:30Z

code update

← Older revision		Revision as of 16:53, 3 February 2022
Line 57:		Line 57:
	Predicates that may lead to errors during runtime are called from within a <vp>try</vp>-construction. For example, see the following code:		Predicates that may lead to errors during runtime are called from within a <vp>try</vp>-construction. For example, see the following code:

	<vip>clauses		<vip>predicates
	~~onControlOK~~(~~_Ctrl, _CtrlType, _CtrlWin, _CtrlInfo~~) = ~~handled(0)~~ :-		onIdc_okClick : button::clickResponder.
	Name = ~~vpi:~~:~~winGetText~~(~~vpi::winGetCtlHandle(thisWin, idc_name)~~),		clauses
	Name "",		onIdc_okClick(_Source) = button::defaultAction :-
	MaleBool = ~~vpi::winIsChecked(vpi:~~:~~winGetCtlHandle~~(~~thisWin, idc_male)~~),		Name = idc_name:getText(),
	Gender = maleFlagToGender(MaleBool),		if Name <> "" then
	OptParent1 = optParent(idc_parent1),		MaleBool = idc_male:getRadioState(),
	OptParent2 = optParent(idc_parent2),		Gender = maleFlagToGender(MaleBool),
	try		OptParent1 = optParent(idc_parent1),
	bl:addPerson(Name, Gender, OptParent1, OptParent2)		OptParent2 = optParent(idc_parent2),
	catch TraceId do		try
	integrityHandler(TraceId))		bl:addPerson(Name, Gender, OptParent1, OptParent2)
	end try,		catch TraceId do
	!,		integrityHandler(TraceId)
	stdIO::write("Inserted ", Name, "\n").		end try,
	~~onControlOK(_Ctrl, _CtrlType, _CtrlWin, _CtrlInfo) = handled(0).~~</vip>		stdIO::write("Inserted ", Name, "\n")
			end if.
			</vip>

	In the above code snippet, the programmer is not sure whether the addition of a person into the database is really possible (because it is not allowed to add an existing person). Thus the <vp>addPerson</vp> is not called directly, but inside a <vp>try</vp>-construction. The <vp>try</vp>-construction has three components ; the first is the code to be called to do the actual work at that point in the code, the second is the a variable (i.e. <vp>TraceId</vp>) bound to a <vp>traceId</vp> which is used to access information about the exception, and the third is the code that is called when the first part terminates with an exception. That component can be used by the programmer to bring the program safely back into control.		In the above code snippet, the programmer is not sure whether the addition of a person into the database is really possible (because it is not allowed to add an existing person). Thus the <vp>addPerson</vp> is not called directly, but inside a <vp>try</vp>-construction. The <vp>try</vp>-construction has three components ; the first is the code to be called to do the actual work at that point in the code, the second is the a variable (i.e. <vp>TraceId</vp>) bound to a <vp>traceId</vp> which is used to access information about the exception, and the third is the code that is called when the first part terminates with an exception. That component can be used by the programmer to bring the program safely back into control.

Thomas Linder Puls: source files

2016-11-03T09:43:32Z

source files

← Older revision		Revision as of 11:43, 3 November 2016
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	In this tutorial, we will continue with the '''family''' example, where we would introduce one more layer - the Data layer - to handle the problem more efficiently. This tutorial will give you all the sophistication that is required to handle complex situations.		In this tutorial, we will continue with the '''family''' example, where we would introduce one more layer - the Data layer - to handle the problem more efficiently. This tutorial will give you all the sophistication that is required to handle complex situations.

	~~'''Download'''~~ source files of the example project used in this tutorial:		The source files of the example project used in this tutorial are part of the installable examples (in the IDE: '''Help -> Install Examples...''').

	* Visual Prolog 7.4 and 7.3 install examples in the IDE:
	*:'''Help -> Install Examples...'''
	* [http://download.pdc.dk/vip/72/tutorial/family4.zip Visual Prolog 7.2 version].
	* [http://download.pdc.dk/vip/71/tutorial/family4.zip Visual Prolog 7.1 version].


	==Concepts==		==Concepts==

EJP: Updated familyDL and familyData code snippets.

2016-11-03T09:40:04Z

Updated familyDL and familyData code snippets.

← Older revision		Revision as of 11:40, 3 November 2016
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	<vip>class familyData		<vip>class familyData
	~~open core~~

	domains		domains
	gender = female(); male().		gender = female; male.

	domains		domains
	person = string.		person = string.
	~~person_list = person*.~~

	domains		domains
	optionalPerson = noPerson(); person(person Person).		optionalPerson =
			noPerson;
	~~predicates~~		person(person Person).
	~~toGender : (string GenderString) -> gender Gender.~~

	~~predicates~~
	~~toGenderString : (gender Gender) -> string GenderString~~.

	end class familyData</vip>		end class familyData</vip>
Line 133:		Line 127:

	predicates		predicates
	person_nd : (person Name) nondeterm ~~(o)~~.		person_nd : (person Name [out]) nondeterm.

	predicates		predicates
Line 139:		Line 133:

	predicates		predicates
	parent_nd : (		parent_nd : (person Person, person Parent [out]) nondeterm.
	person Person,
	person Parent)
	nondeterm ~~(i,o)~~.

	predicates		predicates
Line 155:		Line 146:
	predicates		predicates
	save : ().		save : ().

	end interface familyDL</vip>		end interface familyDL</vip>

Thomas Linder Puls: trap -> try

2016-02-10T09:29:46Z

trap -> try

← Older revision		Revision as of 11:29, 10 February 2016
Line 61:		Line 61:
	If you see the source code that handles the events happening from this dialog in NewPersonDialog.pro, you would see that the code carefully catches a lot of error situations. It even has an integrity checker that attempts to trace what may cause a piece of code to cause an error.		If you see the source code that handles the events happening from this dialog in NewPersonDialog.pro, you would see that the code carefully catches a lot of error situations. It even has an integrity checker that attempts to trace what may cause a piece of code to cause an error.

	Predicates that may lead to errors during runtime are called from within a ~~special built~~-~~in predicate called trap''~~.'' For example, see the following code:		Predicates that may lead to errors during runtime are called from within a <vp>try</vp>-construction. For example, see the following code:

	<vip>clauses		<vip>clauses
Line 80:		Line 80:
	onControlOK(_Ctrl, _CtrlType, _CtrlWin, _CtrlInfo) = handled(0).</vip>		onControlOK(_Ctrl, _CtrlType, _CtrlWin, _CtrlInfo) = handled(0).</vip>

	In the above code snippet, the programmer is not sure whether the addition of a person into the database is really possible (because it is not allowed to add an existing person). Thus the addPerson is not called directly, but ~~through the trap predicate~~. The ~~trap predicate accepts~~ three ~~variables~~; the first ~~of which~~ is the ~~predicate~~ to be called to do the actual work at that point in the code, the second is the ~~error number that~~ is ~~generated in~~ the ~~case an error is triggered~~, and the third is ~~a predicate~~ that is called on the ~~triggering of the error~~. That ~~third predicate~~ can be used by the programmer to bring the program safely back into control.		In the above code snippet, the programmer is not sure whether the addition of a person into the database is really possible (because it is not allowed to add an existing person). Thus the <vp>addPerson</vp> is not called directly, but inside a <vp>try</vp>-construction. The <vp>try</vp>-construction has three components ; the first is the code to be called to do the actual work at that point in the code, the second is the a variable (i.e. <vp>TraceId</vp>) bound to a <vp>traceId</vp> which is used to access information about the exception, and the third is the code that is called when the first part terminates with an exception. That component can be used by the programmer to bring the program safely back into control.

	==The FamilyData Package==		==The FamilyData Package==

Thomas Linder Puls: Reference to tutorials

2013-05-06T13:40:08Z

Reference to tutorials

← Older revision		Revision as of 15:40, 6 May 2013
Line 237:		Line 237:
	Data accessors can also provide a uniform interface to access attributes of the data, while leaving the concrete organization of the attributes hidden.		Data accessors can also provide a uniform interface to access attributes of the data, while leaving the concrete organization of the attributes hidden.

	The advantage of using ''data accessors'' is that algorithms implemented in other areas of the program can be written independent of the knowledge regarding the exact data structure that was used in the Data layer. In the next tutorial in this series, you would see that the data can be easily shifted to a more robust system (using Microsoft's Access database, accessed through an ODBC layer) while retaining everything else exactly the same.		The advantage of using ''data accessors'' is that algorithms implemented in other areas of the program can be written independent of the knowledge regarding the exact data structure that was used in the Data layer.

	There are hardly any pitfalls to this approach, but whatever they are, these pitfalls must be understood. The main one is that two sophisticated levels of understanding have to be reached by the programmer when writing the Data layer''.'' One would be to determine the internal data structures that will remain private within the Data layer. (The kind of thinking, required to develop data structures, was discussed in the Fundamental Visual Prolog tutorial regarding functors). But after that, the programmer will also have to spend time designing efficient ''data accessor'' predicates so that other layers can mate smoothly with the ''Data layer''. Incorrect design of the ''data accessor'' predicates can often create a lot of headache, when a team of programmers is at work. Especially, when the program is required to move from a simple one to a more complex one~~... as you would notice in the next tutorial~~.		There are hardly any pitfalls to this approach, but whatever they are, these pitfalls must be understood. The main one is that two sophisticated levels of understanding have to be reached by the programmer when writing the Data layer''.'' One would be to determine the internal data structures that will remain private within the Data layer. (The kind of thinking, required to develop data structures, was discussed in the Fundamental Visual Prolog tutorial regarding functors). But after that, the programmer will also have to spend time designing efficient ''data accessor'' predicates so that other layers can mate smoothly with the ''Data layer''. Incorrect design of the ''data accessor'' predicates can often create a lot of headache, when a team of programmers is at work. Especially, when the program is required to move from a simple one to a more complex one.

	==Conclusion==		==Conclusion==

Thomas Linder Puls: classInfo

2013-05-06T13:34:33Z

classInfo

← Older revision		Revision as of 15:34, 6 May 2013
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	personExists(Person),		personExists(Person),
	!,		!,
	familyDL_exception::raise_personAlreadyExists(~~classInfo,~~ Person).		familyDL_exception::raise_personAlreadyExists(Person).
	check_personDoesNotExist(_).		check_personDoesNotExist(_).

Thomas Linder Puls: /* The FamilyData Package */ remove classInfo

2013-05-06T13:28:51Z

The FamilyData Package: remove classInfo

← Older revision		Revision as of 15:28, 6 May 2013
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	toGenderString : (gender Gender) -> string GenderString.		toGenderString : (gender Gender) -> string GenderString.

	~~predicates~~
	~~classInfo : core::classInfo.~~
	end class familyData</vip>		end class familyData</vip>

Thomas Linder Puls: 7.4

2012-12-02T22:26:59Z

7.4

← Older revision		Revision as of 00:26, 3 December 2012
Line 5:		Line 5:
	'''Download''' source files of the example project used in this tutorial:		'''Download''' source files of the example project used in this tutorial:

	* ~~[http://download.pdc.dk/vip/74/tutorial/family4.zip~~ Visual Prolog 7.4 ~~version]~~.		* Visual Prolog 7.4 and 7.3 install examples in the IDE:
			*:'''Help -> Install Examples...'''
	* [http://download.pdc.dk/vip/72/tutorial/family4.zip Visual Prolog 7.2 version].		* [http://download.pdc.dk/vip/72/tutorial/family4.zip Visual Prolog 7.2 version].
	* [http://download.pdc.dk/vip/71/tutorial/family4.zip Visual Prolog 7.1 version].		* [http://download.pdc.dk/vip/71/tutorial/family4.zip Visual Prolog 7.1 version].


	==Concepts==		==Concepts==

Thomas Linder Puls: 7.4

2012-12-02T22:01:51Z

7.4

← Older revision		Revision as of 00:01, 3 December 2012
Line 5:		Line 5:
	'''Download''' source files of the example project used in this tutorial:		'''Download''' source files of the example project used in this tutorial:

	* [http://download.pdc.dk/vip/71/~~examples~~/~~tutorial_examples~~/~~fundamental_visual_prolog~~/family4.zip Visual Prolog 7.1 version].		* [http://download.pdc.dk/vip/74/tutorial/family4.zip Visual Prolog 7.4 version].
	* [http://download.pdc.dk/vip/~~72/tutorial_examples~~/~~fundamental_visual_prolog~~/family4.zip Visual Prolog 7.2 version].		* [http://download.pdc.dk/vip/72/tutorial/family4.zip Visual Prolog 7.2 version].
			* [http://download.pdc.dk/vip/71/tutorial/family4.zip Visual Prolog 7.1 version].

	==Concepts==		==Concepts==

Thomas Linder Puls: Category:Fundamental Visual Prolog Tutorial

2011-08-12T08:45:14Z

Category:Fundamental Visual Prolog Tutorial

← Older revision		Revision as of 10:45, 12 August 2011
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	==References==		==References==

	[[Category:~~Tutorials~~]]		[[Category:Fundamental Visual Prolog Tutorial]]