cwb-ccc 0.9.15

CWB wrapper to extract concordances and collocates

Collocation and Concordance Computation

Introduction

This module is a wrapper around the IMS Open Corpus Workbench (CWB). Main purpose of the module is to run queries, extract concordance lines, and calculate collocates.

• Introduction
  • Prerequisites
  • Installation
  • Accessing Corpora
• Usage
  • Queries and Dumps
  • Extracting Concordance Lines
  • Dealing with Anchored Queries
  • Calculating Collocates
  • Defining Subcorpora
  • Extracting Keywords
• Testing
• Acknowledgements

Prerequisites

The module needs a working installation of the CWB and operates on CWB-indexed corpora.

If you want to run queries with more than two anchor points, the module requires CWB version 3.4.16 or later.

Installation

You can install this module with pip from PyPI:

pip3 install cwb-ccc

You can also clone the source from github, cd in the respective folder, and use setup.py:

python3 setup.py install

Accessing Corpora

To list all available corpora, you can use

from ccc import Corpora
corpora = Corpora(registry_path="/usr/local/share/cwb/registry/")
print(corpora)
corpora.show()  # returns a DataFrame

All further methods rely on the Corpus class, which establishes the connection to your CWB-indexed corpus. You can activate a corpus with

corpus = corpora.activate(corpus_name="GERMAPARL1386")

or directly use the respective class:

from ccc import Corpus
corpus = Corpus(
  corpus_name="GERMAPARL1386",
  registry_path="/usr/local/share/cwb/registry/"
)

This will raise a KeyError if the named corpus is not in the specified registry.

If you are using macros and wordlists, you have to store them in a separate folder (with subfolders "wordlists/" and "macros/"). Specify this folder via lib_path when initializing the corpus.

You can use the cqp_bin to point the module to a specific version of cqp (this is also helpful if cqp is not in your PATH).

By default, the data_path points to "/tmp/ccc-data/". Make sure that "/tmp/" exists and appropriate rights are granted. Otherwise, change the parameter when initializing the corpus.

If everything is set up correctly, you can list all available attributes of the activated corpus:

corpus.attributes_available

type	attribute	annotation	active
p-Att	word	False	True
p-Att	pos	False	False
p-Att	lemma	False	False
s-Att	corpus	False	False
s-Att	corpus_name	True	False
s-Att	sitzung	False	False
s-Att	sitzung_date	True	False
s-Att	sitzung_period	True	False
s-Att	sitzung_session	True	False
s-Att	div	False	False
s-Att	div_desc	True	False
s-Att	div_n	True	False
s-Att	div_type	True	False
s-Att	div_what	True	False
s-Att	text	False	False
s-Att	text_id	True	False
s-Att	text_name	True	False
s-Att	text_parliamentary_group	True	False
s-Att	text_party	True	False
s-Att	text_position	True	False
s-Att	text_role	True	False
s-Att	text_who	True	False
s-Att	p	False	False
s-Att	p_type	True	False
s-Att	s	False	False

Usage

Queries and Dumps

The usual starting point for using this module is to run a query with corpus.query(), which accepts valid CQP queries such as

query = r'"\[" ([word="[A-Z0-9]+.?"%d]+ "/"?)+ "\]"'
dump = corpus.query(query)

The result is a Dump object. Its core is a pandas DataFrame (dump.df) similar to a CQP dump and multi-indexed by "match" and "matchend" of the query. All entries of the DataFrame, including the index, are integers representing corpus positions:

dump.df

match	matchend	context	contextend
2313	2319	2293	2339
8213	8217	8193	8237
8438	8444	8418	8464
15999	16001	15979	16021
24282	24288	24262	24308
...	...	...	...

You can provide one or more parameters to define the context around the matches: a parameter context specifying the context window (defaults to 20) and a parameter context_break naming an s-attribute to limit the context . You can specify asymmetric windows via context_left and context_right.

When providing an s-attribute limiting the context, the module additionally retrieves the CWB-id of this attribute, the corpus positions of the respective span start and end, as well as the actual context spans:

dump = corpus.query(
  cqp_query=query,
  context=20,
  context_break='s'
)

dump.df

match	matchend	s_cwbid	s_span	s_spanend	contextid	context	contextend
2313	2319	161	2304	2320	161	2308	2320
8213	8217	489	8187	8218	489	8208	8218
8438	8444	500	8425	8445	500	8433	8445
15999	16001	905	15992	16002	905	15994	16002
24282	24288	1407	24273	24289	1407	24277	24289
...	...	...	...	...	...	...	...

There are two reasons for defining the context when running a query:

1. If you provide a context_break parameter, the query will be automatically confined to spans delimited by this s-attribute; this is equivalent to formulating a query that ends on a respective "within" clause.
2. Subsequent analyses (concordancing, collocation) will all work on the same context.

Notwithstanding (1), the context can also be set after having run the query:

dump.set_context(context_left=5, context_right=10, context_break='s')

Note that this works "inplace".

You can set CQP's matching strategy ("standard", "longest", "shortest", "traditional") via the match_strategy parameter.

By default, the result is cached: the query parameters are used to create an appropriate identifier. This way, the result can be accessed directly by later queries with the same parameters on the same (sub)corpus, without the need for CQP to run again.

We are set up to analyze the query result. Here's the frequency breakdown:

dump.breakdown()

word	freq
[ SPD ]	18
[ F. D. P. ]	14
[ CDU / CSU ]	13
[ BÜNDNIS 90 / DIE GRÜNEN ]	12
[ PDS ]	6

Concordancing

You can access concordance lines via the concordance() method of the dump. This method returns a DataFrame with information about the query matches in context:

dump.concordance()

match	matchend	word
2313	2319	Joseph Fischer [ Frankfurt ] [ BÜNDNIS 90 / DIE GRÜNEN ] )
8213	8217	Widerspruch des Abg. Wolfgang Zöller [ CDU / CSU ] )
8438	8444	Joseph Fischer [ Frankfurt ] [ BÜNDNIS 90 / DIE GRÜNEN ] )
15999	16001	des Abg. Dr. Peter Struck [ SPD ] )
24282	24288	Joseph Fischer [ Frankfurt ] [ BÜNDNIS 90 / DIE GRÜNEN ] )
...	...	...

By default, the output is a "simple" format, i.e. a DataFrame indexed by "match" and "matchend" with a column "word" showing the matches in context. You can choose which p-attributes to retrieve via the p_show parameter. Similarly, you can retrieve s-attributes (at match-position):

dump.concordance(p_show=["word", "lemma"], s_show=["text_id"])

match	matchend	word	lemma	text_id
2313	2319	Joseph Fischer [ Frankfurt ] [ BÜNDNIS 90 / DIE GRÜNEN ] )	Joseph Fischer [ Frankfurt ] [ Bündnis 90 / die Grünen ] )	i13_86_1_2
8213	8217	Widerspruch des Abg. Wolfgang Zöller [ CDU / CSU ] )	Widerspruch die Abg. Wolfgang Zöller [ CDU / CSU ] )	i13_86_1_4
8438	8444	Joseph Fischer [ Frankfurt ] [ BÜNDNIS 90 / DIE GRÜNEN ] )	Joseph Fischer [ Frankfurt ] [ Bündnis 90 / die Grünen ] )	i13_86_1_4
15999	16001	des Abg. Dr. Peter Struck [ SPD ] )	die Abg. Dr. Peter Struck [ SPD ] )	i13_86_1_8
24282	24288	Joseph Fischer [ Frankfurt ] [ BÜNDNIS 90 / DIE GRÜNEN ] )	Joseph Fischer [ Frankfurt ] [ Bündnis 90 / die Grünen ] )	i13_86_1_24
...	...	...	...	...

The format can be changed using the form parameter. The "kwic" format e.g. returns three columns for each requested p-attribute:

dump.concordance(form="kwic")

match	matchend	left_word	node_word	right_word
2313	2319	Joseph Fischer [ Frankfurt ]	[ BÜNDNIS 90 / DIE GRÜNEN ]	)
8213	8217	Widerspruch des Abg. Wolfgang Zöller	[ CDU / CSU ]	)
8438	8444	Joseph Fischer [ Frankfurt ]	[ BÜNDNIS 90 / DIE GRÜNEN ]	)
15999	16001	des Abg. Dr. Peter Struck	[ SPD ]	)
24282	24288	Joseph Fischer [ Frankfurt ]	[ BÜNDNIS 90 / DIE GRÜNEN ]	)

If you want to inspect each query result in detail, use form="dataframe"; here, every concordance line is verticalized text formated as DataFrame with the cpos of each token as index:

lines = dump.concordance(p_show=['word', 'pos', 'lemma'], form='dataframe')

lines.iloc[0]['dataframe']

cpos	offset	word	pos	lemma
2308	-5	Joseph	NE	Joseph
2309	-4	Fischer	NE	Fischer
2310	-3	[	XY	[
2311	-2	Frankfurt	NE	Frankfurt
2312	-1	]	APPRART	]
2313	0	[	ADJA	[
2314	0	BÜNDNIS	NN	Bündnis
2315	0	90	CARD	90
2316	0	/	$(	/
2317	0	DIE	ART	die
2318	0	GRÜNEN	NN	Grünen
2319	0	]	$.	]
2320	1	)	$(	)

Further forms are "slots" (see below) and "dict": In the latter case, every entry in the "dict" column is a dictionary with the following keys:

• "match" (int): the cpos of the match (serves as an identifier)
• "cpos" (list): the cpos of all tokens in the concordance line
• "offset" (list): the offset to match/matchend of all tokens
• "word" (list): the words of all tokens
• "anchors" (dict): a dictionary of {anchor: cpos} (see below)

This format is especially suitable for serialization purposes.

You can decide which and how many concordance lines you want to retrieve by means of the parameters order ("first", "last", or "random") and cut_off. You can also provide a list of matches to get only specific concordance lines.

Anchored Queries

The concordancer detects anchored queries automatically. The following query

dump = corpus.query(
  cqp_query=r'@1[pos="NE"]? @2[pos="NE"] @3"\[" ([word="[A-Z0-9]+.?"%d]+ "/"?)+ @4"\]"',
  context=None, context_break='s', match_strategy='longest'
)
lines = dump.concordance(form='dataframe')

thus returns DataFrames with additional columns for each anchor point:

lines.iloc[0]['dataframe']

cpos	offset	word	1	2	3	4
8187	-24	(	False	False	False	False
8188	-23	Anhaltender	False	False	False	False
8189	-22	lebhafter	False	False	False	False
8190	-21	Beifall	False	False	False	False
8191	-20	bei	False	False	False	False
8192	-19	der	False	False	False	False
8193	-18	SPD	False	False	False	False
8194	-17	--	False	False	False	False
8195	-16	Beifall	False	False	False	False
8196	-15	bei	False	False	False	False
8197	-14	Abgeordneten	False	False	False	False
8198	-13	des	False	False	False	False
8199	-12	BÜNDNISSES	False	False	False	False
8200	-11	90	False	False	False	False
8201	-10	/	False	False	False	False
8202	-9	DIE	False	False	False	False
8203	-8	GRÜNEN	False	False	False	False
8204	-7	und	False	False	False	False
8205	-6	der	False	False	False	False
8206	-5	PDS	False	False	False	False
8207	-4	--	False	False	False	False
8208	-3	Widerspruch	False	False	False	False
8209	-2	des	False	False	False	False
8210	-1	Abg.	False	False	False	False
8211	0	Wolfgang	True	False	False	False
8212	0	Zöller	False	True	False	False
8213	0	[	False	False	True	False
8214	0	CDU	False	False	False	False
8215	0	/	False	False	False	False
8216	0	CSU	False	False	False	False
8217	0	]	False	False	False	True
8218	1	)	False	False	False	False

For an analysis of certain spans of your query matches, you can use anchor points to define "slots", i.e. single anchors or spans between anchors that define sub-parts of your matches. Use the "slots" format to extract these parts from each match:

dump = corpus.query(
    r'@1[pos="NE"]? @2[pos="NE"] @3"\[" ([word="[A-Z0-9]+.?"%d]+ "/"?)+ @4"\]"',
    context=0, context_break='s', match_strategy='longest',
)
lines = dump.concordance(
  form='slots', p_show=['word', 'lemma'], 
  slots={"name": [1, 2], "party": [3, 4]}
)

lines

match	matchend	word	name_word	party_word
8211	8217	Wolfgang Zöller [ CDU / CSU ]	Wolfgang Zöller	[ CDU / CSU ]
15997	16001	Peter Struck [ SPD ]	Peter Struck	[ SPD ]
25512	25516	Jörg Tauss [ SPD ]	Jörg Tauss	[ SPD ]
32808	32814	Ina Albowitz [ F. D. P. ]	Ina Albowitz	[ F. D. P. ]
36980	36984	Christa Luft [ PDS ]	Christa Luft	[ PDS ]
...	...	...	...	...

The module allows for correction of anchor points by integer offsets. This is especially helpful if the query contains optional parts (defined by ?, + or *) – note that this works inplace:

dump.correct_anchors({3: +1, 4: -1})
lines = dump.concordance(
  form='slots', p_show=['word', 'lemma'], 
  slots={"name": [1, 2], "party": [3, 4]}
)

lines

match	matchend	word	name_word	party_word
8211	8217	Wolfgang Zöller [ CDU / CSU ]	Wolfgang Zöller	CDU / CSU
15997	16001	Peter Struck [ SPD ]	Peter Struck	SPD
25512	25516	Jörg Tauss [ SPD ]	Jörg Tauss	SPD
32808	32814	Ina Albowitz [ F. D. P. ]	Ina Albowitz	F. D. P.
36980	36984	Christa Luft [ PDS ]	Christa Luft	PDS
...	...	...	...	...

Collocation Analyses

After executing a query, you can use dump.collocates() to extract collocates for a given window size (symmetric windows around the corpus matches). The result will be a DataFrame with lexical items (e.g. lemmata) as index and frequency signatures and association measures as columns.

dump = corpus.query('[lemma="SPD"]', context=10, context_break='s')

dump.collocates()

lemma	f	marginal	in_nodes	f2	N	f1	z_score	t_score	dice	log_likelihood	mutual_information	log_ratio	O11	O12	O21	O22	E11	E12	E21	E22
die	813	13765	0	13765	149168	5186	15.2882	11.7295	0.0858002	226.513	0.230157	0.870887	813	4373	12952	131030	478.556	4707.44	13286.4	130696
bei	366	1357	0	1357	149168	5186	46.4174	16.6651	0.111875	967.728	0.889744	3.04807	366	4820	991	142991	47.1777	5138.82	1309.82	142672
(	314	1758	0	1758	149168	5186	32.3466	14.2709	0.0904378	574.854	0.710754	2.43408	314	4872	1444	142538	61.1189	5124.88	1696.88	142285
[	221	698	0	698	149168	5186	39.9366	13.2337	0.075119	654.834	0.95938	3.24305	221	4965	477	143505	24.2668	5161.73	673.733	143308
)	207	1827	0	1827	149168	5186	18.0032	9.9727	0.0590332	218.341	0.513075	1.74539	207	4979	1620	142362	63.5178	5122.48	1763.48	142219
...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...

By default, collocates are calculated on the "lemma"-layer, assuming that this is an available p-attribute in the corpus. The corresponding parameter is p_query (which will fall back to "word" if the specified attribute is not annotated in the corpus).

New in version 0.9.14: You can now perform collocation analyses on combinations of p-attribute layers, the most prominent use case being POS-disambiguated lemmata:

dump.collocates(['lemma', 'pos'], order='log_likelihood')

lemma	pos	f	marginal	in_nodes	f2	N	f1	z_score	t_score	dice	log_likelihood	mutual_information	log_ratio	O11	O12	O21	O22	E11	E12	E21	E22
bei	APPR	360	1229	0	1229	149168	5186	48.5376	16.7217	0.112237	1014.28	0.925594	3.16661	360	4826	869	143113	42.7276	5143.27	1186.27	142796
(	$(	314	1758	0	1758	149168	5186	32.3466	14.2709	0.0904378	574.854	0.710754	2.43408	314	4872	1444	142538	61.1189	5124.88	1696.88	142285
Beifall	NN	199	670	0	670	149168	5186	36.406	12.4555	0.0679645	561.382	0.931621	3.14473	199	4987	471	143511	23.2933	5162.71	646.707	143335
[	$(	161	420	0	420	149168	5186	38.3118	11.5378	0.0574385	545.131	1.04242	3.50427	161	5025	259	143723	14.6018	5171.4	405.398	143577
]:	$(	139	479	0	479	149168	5186	29.9811	10.3773	0.0490733	383.895	0.921522	3.09579	139	5047	340	143642	16.653	5169.35	462.347	143520
...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...

For improved performance, all hapax legomena in the context are dropped after calculating the context size. You can change this behaviour via the min_freq parameter.

By default, the dataframe is annotated with "z_score", "t_score", "dice", "log_likelihood", and "mutual_information" (parameter ams). For notation and further information regarding association measures, see collocations.de. Availability of association measures depends on their implementation in the pandas-association-measures package.

The dataframe is sorted by co-occurrence frequency (column "O11"), and only the first 100 most frequently co-occurring collocates are retrieved. You can (and should) change this behaviour via the order and cut_off parameters.

Subcorpora

In cwb-ccc terms, every instance of a Dump is a subcorpus. There are two possibilities to get a dump: either by running a traditional query as outlined above; the following query e.g. defines a subcorpus of all sentences that contain the word "SPD":

dump = corpus.query('"SPD" expand to s')

Alternatively, you can define subcorpora via values stored in s-attributes. A subcorpus of all noun phrases (assuming they are indexed as structural attribute np) can e.g. be extracted using

dump = corpus.query_s_att("np")

You can also query the respective annotations:

dump = corpus.query_s_att("text_party", {"CDU", "CSU"})

will e.g. retrieve all text spans with respective constraints on the party annotation.

Implementation note: While the CWB does allow storage of arbitrary meta data in s-attributes, it does not index these attributes. corpus.query_s_att() thus creates a dataframe with the spans of the s-attribute encoded as matches and caches the result. Consequently, the first query of an s-attribute will be compartively slow and subsequent queries will be faster.

Note also that the CWB does not allow complex queries on s-attributes. It is thus reasonable to store meta data in separate spreadsheets or relational databases and link to text spans via simple identifiers. This way (1) you can work with natural meta data queries and (2) working with a small number of s-attributes also unburdens the cache.

In CWB terms, subcorpora are named query results (NQRs), which consist of the corpus positions of match and matchend (and optional anchor points called anchor and keyword). If you give a name when using corpus.query() or corpus.query_s_att(), the respective matches of the dump will also be available as NQRs in CQP.

This way you can run queries on NQRs in CQP. Compare e.g. the frequency breakdown for a query on the whole corpus

corpus.query('[lemma="sagen"]').breakdown()

word	freq
sagen	234
gesagt	131
sage	69
sagt	39
Sagen	12
sagte	6

with the one a subcorpus:

corpus.query_s_att("text_party", values={"CDU", "CSU"}, name="Union")
corpus.activate_subcorpus("Union")
print(corpus.subcorpus)
> 'Union'

corpus.query('[lemma="sagen"]').breakdown()

word	freq
sagen	64
gesagt	45
sage	30
sagt	12
Sagen	6
sagte	3

Don't forget to switch back to the main corpus when you are done with the analysis on the activated NQR:

corpus.activate_subcorpus()  # switches to main corpus when given no name
print(corpus.subcorpus)
> None

You can access all available NQRs via

corpus.show_nqr()

corpus	subcorpus	size	storage
GERMAPARL1386	Union	82	md-

Keyword Analyses

Having created a subcorpus (a dump)

dump = corpus.query_s_att("text_party", values={"CDU", "CSU"})

you can use its keywords() method for retrieving keywords:

dump.keywords()

lemma	f	f2	N	f1	z_score	t_score	dice	log_likelihood	mutual_information	log_ratio	O11	O12	O21	O22	E11	E12	E21	E22
deswegen	55	92	149800	44023	5.37785	3.77055	0.00249348	36.4851	0.308407	1.02542	55	43968	37	105740	27.0368	43996	64.9632	105712
CSU	255	635	149800	44023	5.00615	4.28257	0.0114201	33.6179	0.135599	0.452701	255	43768	380	105397	186.613	43836.4	448.387	105329
in	867	2498	149800	44023	4.90475	4.51323	0.0372735	33.5751	0.0722588	0.244474	867	43156	1631	104146	734.109	43288.9	1763.89	104013
CDU	260	650	149800	44023	4.99087	4.27789	0.0116401	33.4398	0.133892	0.447052	260	43763	390	105387	191.021	43832	458.979	105318
Wirtschaft	39	64	149800	44023	4.65587	3.23327	0.00176923	27.294	0.316717	1.05277	39	43984	25	105752	18.8082	44004.2	45.1918	105732
...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...

Just as with collocates, the result is a DataFrame with lexical items (p_query layer) as index and frequency signatures and association measures as columns.

New in version 0.9.14: Keywords for p-attribute combinations:

dump.keywords(["lemma", "pos"], order="log_likelihood")

lemma	pos	f	f2	N	f1	z_score	t_score	dice	log_likelihood	mutual_information	log_ratio	O11	O12	O21	O22	E11	E12	E21	E22
F.	NN	161	353	149800	44023	5.62195	4.51279	0.00725617	41.407	0.190883	0.635983	161	43862	192	105585	103.739	43919.3	249.261	105528
deswegen	PROAV	55	92	149800	44023	5.37785	3.77055	0.00249348	36.4851	0.308407	1.02542	55	43968	37	105740	27.0368	43996	64.9632	105712
CSU	NE	255	635	149800	44023	5.00615	4.28257	0.0114201	33.6179	0.135599	0.452701	255	43768	380	105397	186.613	43836.4	448.387	105329
CDU	NE	260	650	149800	44023	4.99087	4.27789	0.0116401	33.4398	0.133892	0.447052	260	43763	390	105387	191.021	43832	458.979	105318
Wirtschaft	NN	39	64	149800	44023	4.65587	3.23327	0.00176923	27.294	0.316717	1.05277	39	43984	25	105752	18.8082	44004.2	45.1918	105732
...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...

Implementation note: dump.keywords() looks at all unigrams at the corpus positions in match..matchend, and compares the frequencies of their surface realizations with their marginal frequencies. Similarly, dump.collocates() uses the the union of the corpus positions in context..contextend, excluding all corpus positions containted in any match..matchend.

Testing

The module ships with a small test corpus ("GERMAPARL1386"), which contains all speeches of the 86th session of the 13th German Bundestag on Feburary 8, 1996.

The corpus consists of 149,800 tokens in 7332 paragraphs (s-attribute "p" with annotation "type" ("regular" or "interjection")) split into 11,364 sentences (s-attribute "s"). The p-attributes are "pos" and "lemma":

corpus.attributes_available

type	attribute	annotation	active
p-Att	word	False	True
p-Att	pos	False	False
p-Att	lemma	False	False
s-Att	corpus	False	False
s-Att	corpus_name	True	False
s-Att	sitzung	False	False
s-Att	sitzung_date	True	False
s-Att	sitzung_period	True	False
s-Att	sitzung_session	True	False
s-Att	div	False	False
s-Att	div_desc	True	False
s-Att	div_n	True	False
s-Att	div_type	True	False
s-Att	div_what	True	False
s-Att	text	False	False
s-Att	text_id	True	False
s-Att	text_name	True	False
s-Att	text_parliamentary_group	True	False
s-Att	text_party	True	False
s-Att	text_position	True	False
s-Att	text_role	True	False
s-Att	text_who	True	False
s-Att	p	False	False
s-Att	p_type	True	False
s-Att	s	False	False

The corpus is located in this repository, but you will have to manually update the path to the binary data files (line 10 of the registry file) in order to make the tests, since the CWB requires an absolute path here.

You can test the module using pytest. Make sure you install all development dependencies:

pip install --dev

You can then simply

make test

and

make coverage

Acknowledgements

The module relies on cwb-python, a Python port of Perl's CWB::CL; thanks to Yannick Versley and Jorg Asmussen for the implementation. Special thanks to Markus Opolka for the implementation of association-measures and for forcing me to write tests.

The test corpus was extracted from the GermaParl corpus (see the PolMine Project); many thanks to Andreas Blätte.

This work was supported by the Emerging Fields Initiative (EFI) of Friedrich-Alexander-Universität Erlangen-Nürnberg, project title Exploring the Fukushima Effect (2017-2020).

Further development of the package is funded by the Deutsche Forschungsgemeinschaft (DFG) within the project Reconstructing Arguments from Noisy Text, grant number 377333057 (2018-2023), as part of the Priority Program Robust Argumentation Machines (SPP-1999).