[OAI-implementers] Some OAI-PMH protocol issues
lac at ecs.soton.ac.uk
Fri Dec 7 08:46:07 EST 2007
I don't think that these are OAI-PMH data transport issues, but
application issues that arise from the interpretation and usage of
metadata from heterogenous data providers.
Managing duplicates: while it makes life inconvenient for your service
users, it is not something that can in general be controlled by
independent data providers. I'm afraid that your service must have the
ability to reconcile duplicate (or near duplicate) items.
Controlled vocabularies for types: you will need to make a
recommendation and try to gain support among the OAI data providers. I
am not sure that the selection that you propose will work in practice.
Is a PDF a text if it has embedded images? Is an image a text if it is
an OCR scan?
Enforced publication dates: what do you enforce if the item has never
been officially published?
On 5 Dec 2007, at 09:40, Frederic MERCEUR wrote:
> Further to the previous email I sent about the document we redacted
> to assess the main difficulties met during the first year of
> management of our Avano harvester, I would like to focus, in this
> email, on just 3 problems linked to the OAI-PMH protocol, Dublin
> Core or to repositories implementation. I would like to focus
> particularly on these 3 problems because I guess they should not be
> so difficult to fix.
> Managing duplicates
> Too many duplicates in a result list in Harvesters list can affect
> the user’s comfort. This is not the main problem harvesters are
> facing today, but this should increase in the coming years. Today,
> at least two phenomenons can generate duplicates in the harvesters’
> Several research organisations or universities can record the same
> electronic resource in their own institutional repository. If Avano
> harvests those repositories, it will get descriptive index files of
> the same topic stored in several places. This can happen if, for
> example, a publication is written in collaboration with several
> institutions. If so, this publication may be archived on the server
> of each institution. Considering the current low auto-archiving
> rate, especially in life sciences, this phenomenon is not the main
> cause of the production of duplicates.
> Projects for national or thematic aggregators can pose problem. In
> some countries, projects of merged institutional repositories can
> agregate records from a selection of repositories in a centralised
> database before displaying them again in OAI-PMH on their own
> server. As a consequence, records referenced on those servers are
> displayed twice in OAI-PMH: via the institutional repository and via
> the centralised database. If the manager of an harvester does not
> know about the architecture of those national or thematic projects,
> he may record the two different servers and generate duplicates in
> his harvester’s result lists.
> To help harvesters administrator to avoid recording repositories
> generating duplicates, could we imagine adding to the description of
> the repository information about the involvement of the said
> repository in a national or thematic agregation system that would
> reexpose the records in OAI-PMH from a different server?
> Managing Type and Date field
> As far as I understand, in order to comply with the OAI-PMH
> protocol, repositories have to expose their data in the non-
> qualified Dublin Core DTD. In this DTD all fields are optional.
> Those fields are also non-qualified, meaning, for example, that they
> do not have to correspond to an enclosed value list. This optional
> and non-formalised information trait raises several issues,
> especially for the Type field.
> Indeed, even if the Dublin Core DTD recommends storing the Type
> information by using standardised text strings, few repositories
> take this into consideration and still present the information as
> free text (ex: publication, artjournal, text, article are used to
> describe an article). Some harvesters, including Avano, offer their
> users to limit their search to one or several types of resources. To
> set up this filter, harvesters try to standardise the Type field
> using a system based on key-word recognition in this character
> string. This standardising is therefore imperfect and the filter
> system may exclude resources from the result list when a user
> narrows his search to one or several types of specific data. Some
> informations contained in this Type field cannot be standardised.
> Even more problematic is the fact that some repositories do not fill
> in this field. As an example, in September 2007, out of the 107.000
> records available in Avano, more than 26.000 did not have a Type
> field. All of those records are automatically barred from the search
> space if a user limits is search to one or several selected types.
> Could it be possible to imagine getting a new normalised and
> mandatory information about the type of the digital object (text,
> image, video….) so harvesters could offer an reliable option to
> filter one or several types ob objects from the end-user search.
> The publication date is also problematic for harvester. For example,
> In September 2007, out of the 107.000 records available in Avano,
> about 15.000 did not have a publication date. When a record does not
> have a publication date or when it cannot be standardised, it is
> automatically located at the end of the list if the user wants the
> results to be sorted by date. In the same way, when a user limits
> his search to a specific period of time (see fig. 9), those files
> are barred from the search even if they correspond to the specified
> But I guess this problem with the publication date will be more
> difficult to fix because it is difficult to define it as mandatory.
> Records without free access to the digital object
> As far as I understand, the OAI-PMH protocol defines only the
> sharing process of bibliographical records contained in a group of
> repositories. As a consequence, some repositories mix records
> without links to the digital object together with records providing
> free access to the resource. Others provide records with paying
> access (ex : BePress) or records with restricted access, for
> example, for university staff.
> In my opinion, this is the major problem harvesters have to face
> today. There is no indication in the Dublin Core DTD showing the
> harvesters the degree of accessibility of the objects described in
> the records. As a consequence, harvesters cannot pass on this
> information to their users or provide them with the ability to
> filter empty records or records offering paying access to the
> It is my opinion that hiding records with free full text among
> records with inaccessible full text is not helpful. For lack of time
> and/or interest, scientists are reluctant to join the Open Access
> movement and the archiving rate of free access publications stays
> very low, especially in life sciences. Free and immediate access to
> documentation is, without doubt, the best way to convince the
> scientists of the interest of the Open Access movement. And drowning
> a minority of records providing free access publications in an ocean
> of records without link to the full text and/or records offering
> paying access to the documents may not be the best way to promote
> the Open Access movement.
> Again, those records without free access to the full text would not
> be a problem for the harvesters if the Dublin Core DTD enabled to
> signify the harvesters the degree of accessibility of the objects
> described in the records. Harvesters could then provide their users
> with the possibility of filtering the records without free access to
> the digital object. But it is still not the case.
> Could we then imagine that, in a possible future version of the OAI-
> PMH, each record will have to provide a normalised and mandatory
> information about the degree of accessibility of the digital object
> (free, paying, impossible, restricted,...)? This will help
> harvesters so much to provide a better service to theirs end-users.
> What do you think?
> Kind regards,
> Fred Merceur
> Ifremer / Bibliothèque La Pérouse
> frederic.merceur at ifremer.fr
> Tél : 02-98-49-88-69
> Fax : 02-98-49-88-84
> Bibliothèque La Pérouse
> Archimer, Ifremer's Institutional Repository
> Avano, a marine and aquatic OAI harvester
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