PPROC, an Ontology for Transparency in Public Procurement

The revised version of the paper looks convincing to me, and the authors have properly addressed all issues raised in the previous round of review. The paper also contains a lot of references to other projects/resources showing that PPROC is sound and widely used, thus worth being presented to the community in detail.

Just a few (minor) remarks:
- I personally do not like starting a subsection right after the beginning of a section. For instance, the title of section 1.1 immediately following that of section 1. In particular, I would not start the introduction with a subsection. Though, this is a personal preference, not a strict requirement.
- A few lines of background about the roles of the Zaragoza City Council and the Provincial Government of Huesca should be added at the beginning of Section 1.2
- In the same section:
- “their semantic relationships” --> “its semantic relationships” ?
- the sequence “—the parties—;” looks quite odd; some blank spaces would make it more clear and readable;
- Section 3.1 (last paragraphs) lists the ontologies reused in PPROC. Some bibliographic references are incorrect (SKOS should refer to [14] instead of [13], GoodRelations to [15]). Also, the references are heterogeneous: some just mention the URLs of the ontologies, others point to bibliographic references, other do not have any reference at all. I would suggest authors to uniform them, and use the same convention throughout the paper.
- Links to UNE 178301 and FOIA could be added in section 5.
- In the conclusion, it is not required to repeat the reference to UNE178301. Also, the part on http://lov.okfn.org/dataset/lov/vocabs/pproc and the Open Contracting standard is not clear.

The paper describes the ontology engineering creation process of the PPROC ontology for transparency in public procurement. The concepts and properties used in the ontology are described in motivated and the alignment to other ontologies is addressed. Moreover, the actual application of the ontology in the generation of machine-readable data from two Spanish public authorities is shown, and some meaningful queries on such kind of data are proposed. A discussion ends the paper.

The paper is well written, motivated, and structured. It shows how Semantic Web, and in particularly ontology engineering, can help in improving the treatment of legal information, and for this reason I believe that the paper well suits the purpose of this special issue and should be accepted. What I appreciate is that, differently from many other papers introducing new ontologies, in this case the ontology is well motivated and not only described, and it has been actually used in real world scenarios, resulting in two SPARQL endpoints and the data they allow to query. In this revised version, the drawbacks I highlighted in my first review have been addressed. For all these reasons, I believe the paper can be accepted for publication on the special issue Semantic Web 4 Legal Domain.

This manuscript was submitted as 'full paper' and should be reviewed along the usual dimensions for research contributions which include (1) originality, (2) significance of the results, and (3) quality of writing.

Overall I am happy with the way my original comments were addressed. I think this is now a solid dataset description and an exemplary paper for practical ontology engineering. However, there are still some minor things I’d like to see addressed (mainly editorial), thus a minor revision (although I am fine if these are only checked by the editor from my side):

1) refernce letter: "A set of SPARQL queries is openly available in GitHub (XXXXXX) and at the Zaragoza city council portal (XXXXX). As an example of use of ontology also has added the result of one of these consultations.”
The authors need to clarify the XXXXXX.

2) the paper contains some stylistic “no-go”s, such as starting a subsection directly after the overall section heading without a lead-in (e.g. section 1, 3, 4) this should be improved.

3) "such as the one established for the TED eSenders or CODICE (https://contrataciondelestado.es/wps/portal/codice)"

please use URIs that are actually references consistently either as footnotes or references, instead of inline in the text.

This paper presents an ontology of e-Procurement that has been used in a real service implemented for the municipality of Zaragoza, in Spain.
I find it significant work, implemented in a concrete context, sufficiently original and with a decent quality of writing, which however needs improvements. State-of-the-art and requirement sections should be improved. Please find a list of required changes in the following:

p.2
In this sentence:

"This means that not only contracting powers and tenderer companies, but also the general public as a whole have been considered in the design of this ontology."

in which sense "have been considered"? ontologies for public data are supposed to do that, then the sentence is redundant, and does not add any special advantage provided by a particular design of the ontology. Alternatively, please explain what special added value is provided by PPROC for the general public, or explain how transparency is specially supported by PPROC (see also the other comments below).

p.3
In this sentence:

"The announcements that are published on these web sites are among the first exchanges of information performed electronically using structured messages."

"first" among what?

p.3
The following sentence:

"This perspective has determined the semantic relationships of the model. Some systems of legal concepts are organised vertically from the most general concepts to the most specific ones. In this case, the relationships are about belonging. Other systems,
known as operational families, gather together the elements related to a specific item
[5]. An institution-based model belongs to this second type and their semantic
relationships are organised according to the role that each concept plays within the
“institution” that is represented. In order to identify and define these relationships, the science of the law can be used, which is devoted to studying and organizing the legal
elements that comprise institutions and the relationships between them."

is almost incomprehensible to me. The authors should try to make it clear how those abstract legal distinctions end up into requirements for the ontology they have developed. In those terms, I fail to see any formal ontological distinction ("general to specific" refers to classes? ontology modules?; and how "institution-based" impacts on PPROC design? also: isn't it true for any domain to "gather together the elements related to a specific item"? what is specific to "gather together" here? sets, concepts, else?

p.5
criterions -> criteria

p.5
These claims/motivations for improving over the state-of-the-art:

"After studying these ontologies, the decision to develop the PPROC ontology was
taken. On the one hand, because two of them (PCO and MOLDEAS) had not the degree of detail required for project purposes. On the other hand, LOTED2 model was considered too complex. In addition, we consider that their model was excessively centered in legal texts. Nevertheless, the main reason for undertaking a new development was that the main objective we chased with the use of the ontology was to improve the transparency of public contracting processes. Under this perspective, none of the three ontologies studied was satisfactory, because they had not transparency as its primary goal. In consequence, they did not detail many of the public procurement concepts that are necessary for transparency purpose and they were not designed to facilitate the understanding by citizenship of the information provided in the buyers profile."

should be supported more objectively in the requirements section, or at least with examples in the state-of-art section. Saying simply that one ontology is too lightweight and another too complex is way too generic. Also, the requirements about transparency -- which are considered the main contribution of PPROC by the authors themselves -- are not evident in the following section, and no reason is given for the claimed lack of this coverage in existing ontologies.
The current narrative leaves the impression that there is some special sense of how transparency is supported, but it is not explained, therefore the reader remains with the intuition that any public procurement ontology can bring transparency simply because it enables the publishing of linked data with an explicit schema.

The mention of "Ontology 101" as the methodology of choice is almost redundant, since the few techniques applied for the design of PPROC are actually supported by most existing methods. As I said, I'd rather see more detail into the requirements, and their associated solutions instead.

Overall: please revise English with the help of a skilled writer or native speaker.