Gringo Wrapper

A wrapper for gringo that takes a logic program as input and outputs the grounded program without any optimizations. For example, calling gringo with the logic program

a.
b :- a.

leads to the grounded output a. b. Calling gringo-wrapper with the same logic program does not perform any optimizations.

Furthermore, (unless the --no-debug option is present) the gringo-wrapper adds a new unique atom _debug#(V1, ...) to the body of each non-fact rule of the logic program, where # is an integer starting from 1 to the number of non-fact rules in the logic program, and (V1, ...) is the list of all variables used in the rule (if any). In addition to adding the _debug atoms to the body of the rules, one choice rule containing all debug atoms is added to the program. The prefix of the debug atoms can be specified using the --debug-constant option.

Table of contents

• Usage
• Building
• How it works
• Assertions
• Debug atom map
• Performance analysis

Usage

Make sure that you have added the location of the gringo binaries to your PATH system variable. Download the gringo-wrapper-X.X-bin.zip or gringo-wrapper-X.X-bin.tar.gz file from the latest gringo-wrapper release, or build it yourself. Unpack the archive and use the scripts provided in the bin/ directory to start the gringo-wrapper:

gringo-wrapper [options] [files]

• If you specify one or more files, gringo-wrapper will read the contents of that files and print the grounded program on the standard output.
• If you do not specify a filename, use the standard input to specify the logic program to ground. Note that the input has to be delimited by EOF (which can be done in the console using CTRL+D on Unix machines and CTRL+Z on Windows machines).
• Call gringo-wrapper -h for all options.

Building

This project is managed using Apache Maven. To build it, clone the repository and execute the package goal from maven:

git clone https://github.com/gaste/gringo-wrapper
cd gringo-wrapper
mvn package

This will create a .zip and .tar.gz file containing the Java archive as well as start scripts for Windows and Unix in the target/ directory.

How it works

The gringo-wrapper replaces each fact f of the logic program with the rule f :- _l, where _l is a fresh atom. Adding the rule _l | -_l ensures that gringo cannot do any optimization, since there are no facts in the logic program. After this modification, the gringo-wrapper uses gringo to ground the modified logic program. Then it replaces each grounded rule f :- _l with the fact f. and removes the artificial atom _l.

Assertions

The gringo-wrapper rewrites assertions of the form assertTrue(atom) and assertFalse(atom) to rules :- not atom and :- atom, respectively. Furthermore, one can use the fixModel(atom1,atom2,...) command to fix the expected answer set { atom1, atom2, ... }.

Debug atom map

Unless the --no-debug option is present, the gringo-wrapper also appends a mapping of the debug predicate symbols to the rules at the end of the ground program. The entries of the debug atom map are of the following form:

10 _debug# #vars variables rule

For example, consider the following preprocessed logic program:

a :- b, _debug1.
pred(X,Y) :- n(X), n(Y), _debug2(X,Y).

The debug atom map of this program is

10 _debug1 0 a :- b.
10 _debug2 2 X Y pred(X,Y) :- n(X), n(Y).

Performance analysis

We have assessed the performance of the gringo-wrapper by comparing it with the OUROBOROS [1,2] debugger. We used the same instances and encodings of the second ASP competition that where used in the evaluation of [2]. Both the program encodings as well as the OUROBOROS translator can be found here inside the project org.mmdasp.sealion.ouroboros. For the OUROBOROS translator, we used the code of the org.mmdasp.sealion.ouroboros.evaluation.EvaluationEA class. The encodings of the instances where taken from the org.mmdasp.sealion.ouroboros.evaluation.programs package.

All benchmarks where performed on a machine equipped with an Intel Core i7-3667U CPU, 8GB of RAM as well as a 256 GB Toshiba THNSNF256GMCS solid-state drive. The grounders gringo, gringo-wrapper, and OUROBOROS where executed using the following commands, respectively:

gringo program.lp instance.in > grounded.txt
gringo-wrapper -nw program.lp instance.in > grounded.txt
java -jar ouroboros-translator.jar program.lp | gringo instance.in > grounded.txt

The results of the benchmark are presented below. Each row contains the identifier of the instance, the number of non-grounded rules (#ng), the number of grounded rules by gringo 4.4 (#g g), gringo-wrapper (#g g-w), and OUROBOROS (#g o) as well as the time in seconds required for the grounding (t). Furthermore, we report the increase of the size of the grounded program (inc) for the gringo-wrapper and OUROBOROS, compared to gringo.

Program	Instance	#ng	#g g	t	#g g-w	t	inc	#g o	t	inc
Graph Coloring	1-125	1672	6145	0.22	8031	0.63	1.3	19020	0.95	3.1
Graph Coloring	11-130	1757	6455	0.21	8416	0.68	1.3	19845	1.10	3.1
Graph Coloring	21-135	1986	7269	0.24	9305	0.73	1.3	21174	1.04	2.9
Graph Coloring	30-135	1794	6597	0.25	8633	0.64	1.3	20502	1.02	3.1
Graph Coloring	31-140	2039	7467	0.22	9578	0.67	1.3	21887	1.03	2.9
Graph Coloring	40-140	2219	8097	0.32	10208	0.68	1.3	22517	1.03	2.8
Graph Coloring	41-145	2262	8260	0.25	10446	0.68	1.3	23195	1.04	2.8
Graph Coloring	51-120	2405	8773	0.36	11034	0.76	1.3	24223	1.05	2.8
Hanoi	09-28	104	31748	0.40	94166	1.61	3.0	1739800	8.09	54.8
Hanoi	11-30	106	34056	0.33	100942	1.58	3.0	1864222	9.50	54.7
Hanoi	15-34	110	38672	0.38	114524	2.11	3.0	2112986	9.43	54.6
Hanoi	16-40	100	27137	0.35	80615	1.40	3.0	1491281	7.04	55.0
Hanoi	22-60	102	28311	0.29	84644	1.43	3.0	1678483	7.80	59.3
Hanoi	38-80	106	34044	0.23	100942	1.68	3.0	1864250	8.53	54.8
Hanoi	41-100	104	31738	0.39	94166	1.52	3.0	1739830	13.24	54.8
Hanoi	47-120	99	25968	0.19	77227	1.49	3.0	1429695	6.90	55.1
Knights Tour	01-8	21	1384	0.34	3413	1.14	2.5	12985716	59.44	9382.7
Knights Tour	03-12	22	3356	0.13	8652	0.60	2.6	>72244034	>300	>21526.8
Knights Tour	05-16	21	6192	0.16	16285	0.64	2.6	>69494641	>300	>11223.3
Knights Tour	06-20	21	9892	0.16	26321	0.88	2.7	>62785993	>300	>6347.1
Knights Tour	07-30	21	22922	0.40	61911	1.13	2.7	>59166564	>300	>2581.2
Knights Tour	08-40	21	41352	0.44	112501	1.27	2.7	>54944042	>300	>1328.7
Knights Tour	09-46	21	55002	0.53	150055	1.58	2.7	>56443633	>300	>1026.2
Knights Tour	10-50	22	65182	0.86	178094	2.15	2.7	>62402315	>300	>957.4
Partner Units	176-24	68	12563	0.22	14218	1.03	1.1	102023	1.47	8.1
Partner Units	23-30	117	39231	0.29	42106	1.20	1.1	276645	2.11	7.1
Partner Units	29-40	108	59979	0.34	64413	1.67	1.1	629639	3.35	10.5
Partner Units	207-58	136	158564	0.61	168289	3.07	1.1	2726182	11.94	17.2
Partner Units	204-67	141	218808	0.78	231083	5.30	1.1	4280282	17.79	19.6
Partner Units	175-75	290	682015	2.10	699472	16.03	1.0	8604415	40.60	12.6
Partner Units	52-100	254	952363	2.68	979603	16.61	1.0	20125857	90.10	21.1
Partner Units	115-100	254	952369	2.86	979759	16.07	1.0	20317011	94.26	21.3

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References

[1]: Oetsch, J., Pührer, J., Tompits, H.: Catching the Ouroboros: On Debugging Non-ground Answer-Set Programs. TPLP 10(4-6), 2010 (2010)
[2]: Polleres, A., Frühstück, M., Schenner, G., Friedrich, G.: Debugging Non-ground ASP Programs with Choice Rules, Cardinality and Weight Constraints. In: LPNMR, pp. 452–464 (2013)