[Building Sakai] Resources Access via Database

Thu Jan 26 05:57:29 PST 2012

BTW, for developers working on tools in Sakai, there are two versions of the file picker.  One makes links (as in ePortfolio) and the other makes copies (as in other apps).  If you want to link to files instead of creating copies, you can do so using the file picker the way ePortfolio does.  

On Jan 26, 2012, at 8:53 AM, Jim Eng wrote:

> This is not a bug.  It is the intended behavior of the resources tool most places in sakai. 
> 
> Matthew described how file-copying is implemented in most places in Sakai.  In the ePortfolio apps, most copies are actually links rather than copies.  
> 
> Years ago, we had a lengthy discussion of using links instead of copies.  Three major approaches were discussed:
> 
> 1) Copying (or duplicating) results in a completely separate copy of a file (the current behavior).
> 2) Copying results in a link to an existing file (as in ePortfolio).
> 3) Copying results in a link to a record identifying the current version of a file, which may be used in multiple locations in sakai (similar to what Matthew described as an alternative, I think). 
> 
> The decision to stay with that first approach was based on user expectations.  When users make a copy of a file, they expect it to be an independent entity.  It would be considered a bug if a change to the original also changed the copy, or vice versa.  
> 
> The second approach was used in ePortfolio because the app requires that behavior.  Users may place links to a file in several places with the expectation that other users will access them and changes made from any entry point will be available no matter where the file is accessed from.  
> 
> The third approach was discussed as a way to avoid having multiple exact copies of the same file in the multiple locations in the file system and yet preserve the behavior of the first approach.  The idea is that we have an index that lets us find whether a particular file already exists in the file system.  If I upload a file and there's already an identical file in the system, we would just link to the existing file instead of saving a new copy in the file system. If I later revise my file so it is no longer identical to the other file, a new copy is created with my changes.  This requires a new layer that keeps track of the actual file contents. It might have made sense to implement something along those lines years ago, but it wouldn't make sense now.  It might make sense to take advantage of some file management systems that provide this functionality, as Matthew describes.  
> 
> Jim
> 
>  
> On Jan 25, 2012, at 1:42 PM, Matthew Jones wrote:
> 
>> There is no concept of file links (symlinks or otherwise) in the Sakai file system. All files are copied as is. There may be duplicate content across multiple sites (in the file system) if a site is duplicated and content is copied.
>> 
>> Some file systems (lessfs/zfs) and hardware like netapp filer [1] support file de-duplication at a lower level which some places probably use to work around this problem. Most of the time storage is so inexpensive that it doesn't become that big of an issue though it would have been a nice feature to have in the system.
>> 
>> http://serverfault.com/questions/23212/block-level-deduplication-on-linux 
>> 
>> On Wed, Jan 25, 2012 at 12:56 PM, Jeff Davidson <jdavidso at usouthal.edu> wrote:
>> A follow up question is when someone "dupes"
>> (copies) content from one site to another, does
>> Sakai (we have a hosted site) truly copy the
>> content or just put in pointers to an "absolute"
>> storage location, i.e., are there two copies of the
>> content as a result of "duping" or just one with
>> multiple sets of pointers?
>>  
>> Thanks,
>>  
>> Jeff
>>  
>> Jeff Davidson
>> Manager, Learning Management System Services
>> Innovation in Learning Center
>> University of South Alabama
>> (251) 380-2845
>> (251) 380-2713 (fax)
>>  
>> 
>> 
>> >>> Jez Cope <j.cope at bath.ac.uk> 1/25/2012 9:19 AM >>>
>> 
>> Future-proofing would be good!
>> 
>> Not very important, but I think Jackrabbit and kin are JSR 170 (yes, 
>> there are far too many JSRs to remember!) – IIRC 168 is portlets.
>> 
>> What other functionality might be useful for this type of integration?
>> 
>> Jez
>> 
>> Adam Marshall wrote:
>> > Cambridge did some work a while ago integrating Sakai 2.5 (?) with a JSR 168 repo (Jackrabbit) and I think they also integrated with DSpace around the same time.  I would have thought their work would be useful to build upon.
>> >
>> > Would it make sense to look at what the OAE crew are doing about underlying repos so that any work is future-proofed?
>> >
>> > Adam
>> >
>> >> -----Original Message-----
>> >> From: sakai-dev-bounces at collab.sakaiproject.org [mailto:sakai-dev-
>> >> bounces at collab.sakaiproject.org] On Behalf Of Jez Cope
>> >> Sent: 25 January 2012 14:30
>> >> To: sakai-dev at collab.sakaiproject.org
>> >> Subject: Re: [Building Sakai] Resources Access via Database
>> >>
>> >> We have plans to develop a basic interface between Sakai and a digital
>> >> repository (such as DSpace/Fedora) via the SWORD2 protocol which,
>> >> depending on how it's implemented, may allow exactly this type of shared
>> >> resource usage. I'll add this as a possible use case — happy to discuss
>> >> further on- or off-list.
>> >>
>> >> There's already been some work done to allow static "mounting" of Fedora
>> >> content within Resources by Cambridge and later Hull (in the UK). See
>> >> blog post linked below for some info and links. Hull's Chris Awre may be
>> >> the most up-to-date on this (he presented the work at EuroSakai 2011).
>> >>
>> >> All the best,
>> >> Jez
>> >>
>> >> Refs:
>> >> DSpace - http://www.dspace.org/
>> >> Fedora - http://fedora-commons.org/
>> >> SWORD - http://swordapp.org/
>> >> Iridium project blog post -
>> >> http://iridiummrd.wordpress.com/2011/11/22/research-data-management-
>> >> at-euro-sakai-2011/
>> >>
>> >> Jeff Davidson wrote:
>> >>> In follow up to this need, we were wondering
>> >>> if it's possible to build a repository of files within
>> >>> a project site under Resources and then access it
>> >>> from multiple course sites and/or project sites
>> >>> within Sakai
>> >>>
>> >> --
>> >> Jez Cope<http://people.bath.ac.uk/jc619>, ICT Project Manager
>> >> Centre for Sustainable Chemical Technologies
>> >> <http://www.bath.ac.uk/csct>
>> >> University of Bath
>> >> Tel: +44(0)1225 385827
>> >> Skype: jezcope
>> >>
>> >>
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>> 
>> -- 
>> Jez Cope <http://people.bath.ac.uk/jc619>, ICT Project Manager
>> Centre for Sustainable Chemical Technologies
>> <http://www.bath.ac.uk/csct>
>> University of Bath
>> Tel: +44(0)1225 385827
>> Skype: jezcope
>> 
>> 
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