W3C home > Mailing lists > Public > public-lod@w3.org > December 2009

Re: Linked Data with web2py

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Thu, 24 Dec 2009 13:51:04 -0500
Message-ID: <4B33B818.6050203@openlinksw.com>
To: Massimo Di Pierro <MDiPierro@cs.depaul.edu>
CC: "public-lod@w3.org" <public-lod@w3.org>, Chris Baron <topher.baron@gmail.com>
Massimo Di Pierro wrote:
> Good. I think we agree.

Happy Holidays to You, and of course everyone else on the mailing list!

> Massimo
> On Dec 24, 2009, at 12:24 PM, Kingsley Idehen wrote:
>> Massimo Di Pierro wrote:
>>> You say "ODBC is about making the backend DBMS engines
>>> interchangeable". Does it mean there is a way to write an arbitrary
>>> SQL query once and it is guaranteed to work when I change the database
>>> from Oracle to PostgreSQL and vice versa (that is what web2py 
>>> provides)?
>> You are providing a Virtualization layer atop the Data Access Drivers.
>>> If so, would you provide an example of how you would do pagination
>>> which is highly dialect dependent? I guess I am missing this.
>> Virtuoso would do that for you. Microsoft JET engine would do that for
>> you. In either case you link the ODBC DSN into the Virtual DBMS.
>>> What is the license of Virtuoso?
>> Dual i.e. Open Source and Commercial. The Virtual DBMS isn't Open 
>> Source.
>>> We do not provide nor created an ODBC driver. We use pyODBC for those
>>> back-ends that require ODBC. For those RDBS that do not, I guess, you
>>> can still use pyODBC but currently it would require some minor
>>> modification to our source code.
>> As long as you don't have any DBMS specific code in your ODBC calls to
>> pyODBC then you're set re. your obligations :-)  Then matters go down to
>> the pyODBC layer where they should work like Virtuoso, Access and other
>> ODBC apps re. use of Metadata calls to deduce underlying DBMS
>> capabilities via the ODBC Drivers for those DBMS engines.
>>> Bare in mind that the web2py user, whether he/she wishes to develop a
>>> generic web app or expose existing data using Linked Data, the user
>>> never writes any SQL. Not even our RDF plugin contains any SQL code.
>> The abstraction and its goals are crystal clear to me.
>>> Our approach is similar to SQLAlchemy, SQLObject, Django ORM and Ruby
>>> Active Record. It is an approach typical of interpreted languages
>>> which provide introspection capabilities. It has some similarities
>>> with Java Hibernate.
>> We built a fixed ODBC Layer for Ruby Active Record [1]. An OpenLink
>> member of staff is now the PHP-ODBC maintainer etc..
>>> Anyway. The DAL is one component of web2py. Other components include
>>> web server, libraries to handle cookies, create session, cache web
>>> based and database queries, generate web forms from database models,
>>> validate all input fields, report errors on validation,
>>> internationalization, web based IDE, web based testing and debugging,
>>> automatic generation of a web based interface to any database, role
>>> based access control system, a template language to render data in
>>> HTML/XML and other protocols, ability to serialize data in XMl, CSV,
>>> JSON, RSS, RTF and generate services in XMLRPC, JSONRPC for Google Web
>>> Toolkit, and AMFRPC for Flash/Flex.
>>> We tried hard to build this thing so that (at least in the default
>>> configuration) it does not have any third party dependence, requires
>>> no installation (just unzip and click) and no configuration, to be
>>> super easy to setup. Requiring ODBC or any other third party product
>>> would not simplify our work. It would increase complexity, setup
>>> costs, and reduce portability.
>> Again, not questioning your vision and goals re. your tech.
>>> I would agree that ODBC should be an option for all database that
>>> provide the driver.
>> Yep! That's what I am preoccupied with and very protective of etc.. :-)
>>> We are in the process of re-factoring our source for the purpose of
>>> making it easier to plugin more non-relational databases. This will be
>>> completed in one month or so. Once done it will be straightforward to
>>> use the ODBC drivers for those RDBMS database back-ends that currently
>>> do not use it, if you wish to do so.
>> Great!
>> Links:
>> 1. http://odbc-rails.rubyforge.org/
>> Kingsley
>>> You can find more DAL example here:
>>> http://www.web2py.com/examples/default/dal although the best reference
>>> is the web2py book
>>> http://www.amazon.com/s/ref=nb_ss?url=search-alias%3Daps&field-keywords=9780470592359 
>>> Massimo
>>> On Dec 24, 2009, at 11:19 AM, Kingsley Idehen wrote:
>>>> Massimo Di Pierro wrote:
>>>>> I think we are talking apples and oranges.
>>>>> According to Microsoft, who proposed ODBC,
>>>>>    http://msdn.microsoft.com/en-us/library/aa198030%28SQL.80%29.aspx
>>>>> "The driver passes SQL statements to SQL Server and returns the
>>>>> results of the statements to the application."
>>>> No, before an ODBC app talks to an ODBC Driver, it should use ODBC
>>>> metadata calls to understand the capabilities of the underlying 
>>>> driver.
>>>> That's how ODBC applications are supposed to be written.
>>>> ODBC is not a simple CLI (as per what you get from DBMS vendors) for
>>>> executing SQL statements, far from it.
>>>>> The purpose of the web2py DAL is that of generating the SQL 
>>>>> statements
>>>>> (in the case of RDBS) and it does not care whether the connection is
>>>>> established via ODBC or not.
>>>> Its an abstraction that sits atop data access APIs.
>>>> Putting my question differently, what happens when I use ODBC 
>>>> against a
>>>> DBMS that isn't DB2 or MS SQL Server re. this interface? Basically, 
>>>> can
>>>> I substitute either via the ODBC hook ?
>>>>> We do not use ODBC on Oracle, for example, but we use cx_Oracle
>>>>> instead because, according to this is a quote from the Oracle web 
>>>>> page:
>>>>> http://www.oracle.com/technology/pub/articles/rubio-python-turbogears.html 
>>>>> "cx_Oracle serves as the core and lowest-level API for bridging a
>>>>> Python environment to an Oracle database. cx_Oracle is to Python what
>>>>> an Oracle JDBC driver is to Java, enabling an application to execute
>>>>> raw SQL queries and manipulate database cursors with a fine level of
>>>>> detail."
>>>> Yes, what do you expect Oracle to say? Something like: we have an
>>>> interface that lacks the deductive capabilities of the ODBC interface
>>>> that ultimately makes DBMS swapping nice and easy?
>>>>> We could use pyODBC on Oracle as we do with with DB2 but the
>>>>> installation process would be more cumbersome.
>>>> Depends on which ODBC drivers you use. In fact, you can install our
>>>> Drives using an installer on any platform we support (and thats a vast
>>>> array of platforms).
>>>> Post installation we even give you basic connection exercisers or a
>>>> platform port of the ODBC Driver Manager that verifies DSNs post
>>>> creation.
>>>>> ODBC does a lot but in the end it just gives a connection and a 
>>>>> cursor
>>>>> object. It does not give us complete database abstraction which is
>>>>> what the web2py DAL does.
>>>> Of course it gives you complete DBMS abstraction. What you really mean
>>>> is this: the interface you are using doesn't really exploit ODBC to 
>>>> the
>>>> max. I believe this ODBC layer comes from someone else, right?
>>>>> One of the most important issue from our prospective is that the
>>>>> web2py DAL works with Non Relational Databases too. Currently only
>>>>> Google Big Table on the Google App Engine but we are working on
>>>>> MongoDB and CouchDB support.  ODBC does not work with non-relational
>>>>> databases.
>>>> Virtuoso provides an ODBC interface that actually lets you work with
>>>> XML, RDF, Web Services and other data representations and model
>>>> combinations.  Jena, Redland, and Sesame abstractions all work with
>>>> Virtuoso via its JDBC or ODBC drivers. Again, ODBC capabilities are 
>>>> very
>>>> dependent on who's ODBC implementation (app or driver) you are working
>>>> with.
>>>> In our world you can join a relation table and Web Addressable 
>>>> Resource
>>>> via SPARQL pattern in Procedure Views (Table Valued Functions in 
>>>> Oracle
>>>> parlance) executed inside the Virtuoso SQL (i.e., SPASQL [1]).
>>>> Naturally, you can also to the opposite i.e., surface SQL 
>>>> functionality
>>>> in SPARQL[2] etc..
>>>>> Running on the Google App Engine cloud has some limitations. We can
>>>>> only upload pure Python or pure Java programs, no C/C++ modules or
>>>>> pre-compiled modules. We can only use the Google API or something 
>>>>> that
>>>>> they call GQL. There is no SQL on GAE because it is not a relational
>>>>> database. Hence, ODBC is not option. Building our system on ODBC
>>>>> simply would not cut it. Yet the Google App Engine is the single best
>>>>> thing that happened to the world of web development in some time
>>>>> (practically free, unlimited scalability, zero maintenance, no 
>>>>> messing
>>>>> up with server or database administration). We use ODBC when we can
>>>>> but we are interested in pushing our technology in places where ODBC
>>>>> is not an option.
>>>>> Least but not last I want to make the case that everybody is doing 
>>>>> web
>>>>> apps with database connections these days. This is now off-the-shelf
>>>>> technology and people should not pay for it. Most ODBC drivers are
>>>>> commercial products or require a commercial license for enterprise
>>>>> use. Our Database Abstraction Layer is released under the GPL2
>>>>> license, only requires third party GPL or BSD drivers, and has been
>>>>> tested by more than 1500 registered users and 50 developers.
>>>> I am not questioning your vision. And when it comes to data access, I
>>>> think REST based Open Data Access (Linked Data) is something I 
>>>> advocate
>>>> strongly,  as a superior solution to ODBC, JDBC, ADO.NET, OLE-DB, or
>>>> XMLA when dealing disparately shaped data sources.
>>>> My fundamental point to you is this: ODBC is a DBMS independent 
>>>> API, so
>>>> you shouldn't speak in DBMS specific terms re. ODBC. You have Native
>>>> CLIs from DBMS vendors that occupy the Database Specific Data 
>>>> Access API
>>>> box :-)
>>>> ODBC is about making the backend DBMS engines interchangeable, one 
>>>> size
>>>> doesn't fit all re. ODBC Drivers  or ODBC compliant applications. I
>>>> should be able to simply slot in our Virtuoso ODBC Driver, or our ODBC
>>>> Drivers for all the other DBMS engines we support without issue via 
>>>> your
>>>> ODBC hook.  Same should apply to any other ODBC Driver vendor.
>>>> To conclude; when I have a moment I'll have your ODBC layer tested
>>>> against our ODBC Drivers, if there are issues, we'll make a simply
>>>> report highlight ODBC APIs issues etc. (for you or whoever is 
>>>> behind the
>>>> ODBC layer. Worst case we can fix it ourselves as we already done many
>>>> other interfaces).
>>>> Links:
>>>> 1. http://docs.openlinksw.com/virtuoso/rdfsparql.html#rdfsparqlinline
>>>> 2. http://docs.openlinksw.com/virtuoso/rdfsparql.html#rdfsqlfromsparql
>>>> Kingsley
>>>>> Massimo
>>>>> On Dec 24, 2009, at 9:30 AM, Kingsley Idehen wrote:
>>>>>> Massimo Di Pierro wrote:
>>>>>>> Hi Kingsley,
>>>>>>> Internally we use the Python ODBC driver for the connection to DB2
>>>>>>> and
>>>>>>> to MSSQL.
>>>>>> But how have you come to conclude that ODBC only works with DB2 and
>>>>>> MSSQL? What about ODBC Drivers that have been developed to work
>>>>>> consistently across:
>>>>>> Virtuoso, Oracle, SQL Server, DB2, Informix, Ingres, Sybase, 
>>>>>> Progress,
>>>>>> MySQL, Firebird, other ODBC Drivers, JDBC Drivers etc? Thus, you 
>>>>>> could
>>>>>> have the option ODBC as opposed to: ODBC for DB2 and MS SQL Sever.
>>>>>> What about the fact that you have ODBC Drivers for Virtuoso that
>>>>>> enable
>>>>>> to make one ODBC connection to all the DBMS engines above, and treat
>>>>>> their tables as though they were part of one DBMS i.e., Virtual DBMS
>>>>>> based Relational Data Virtualization (or Federation).
>>>>>>> We use more specific drivers for the other databases, as 
>>>>>>> recommended
>>>>>>> by the official documentation.
>>>>>> What official documentation? URL please.
>>>>>>> Anyway, from the Python programming point of view they all 
>>>>>>> expose the
>>>>>>> same Python API.
>>>>>>> The fact is ODBC only unifies the data access API and that is a 
>>>>>>> small
>>>>>>> part of we needed since different database still have different
>>>>>>> dialects.
>>>>>>> Our DAL completely abstracts the database and writes the SQL in the
>>>>>>> specific dialect of specific backend.
>>>>>> Are you aware of the fact that via ODBC metadata calls you can
>>>>>> deductively discern the capabilities and SQL dialiects supported 
>>>>>> by an
>>>>>> DBMS. This is all about the ODBC Drivers you are working with, 
>>>>>> not the
>>>>>> ODBC spec itself (which is vast and very sophisticated).
>>>>>>> For example a limit query in SQLite is done with "SELECT ...
>>>>>>> FIRST N"
>>>>>>> The same query in MSSQL is done with "SELECT .... TOP N", in
>>>>>>> Oracle it
>>>>>>> requires two nested selects "SELECT ... FROM (SELECT w_tmp.*, 
>>>>>>> ROWNUM
>>>>>>> w_row FROM (SELECT ...) w_tmp WHERE ROWNUM<=N)...;".  In the 
>>>>>>> case of
>>>>>>> the Google App Engine there is not even SQL so our DAL translates
>>>>>>> directly into Google API calls.
>>>>>> Again, you should focus on the functionality you want, and then 
>>>>>> see if
>>>>>> the underling ODBC Driver can handle what you want, if it can't you
>>>>>> can
>>>>>> drop back to your work arounds.
>>>>>>> The same query in the web2py DAL reads like, for example:
>>>>>>>  db=DAL('postgresql://username:password@localhost', pool_size=100)
>>>>>>>  db.define_table('person',Field('name'))
>>>>>>>  db.person.insert(name='Ken')
>>>>>>>  rows = db(db.person.name=='Ken').select(limitby = (0,10))
>>>>>>> The first line choose the most appropriate connection driver (which
>>>>>>> may be ODBC). The second line tried to define a table "person". 
>>>>>>> If it
>>>>>>> does not exist, it is CREATEd. If it exists and has a different
>>>>>>> stricture, it is ALTERed. The third line inserts a second. The 
>>>>>>> forth
>>>>>>> line is performs the limit query.
>>>>>>> As you can see we do not use raw SQL anywhere in our system, 
>>>>>>> although
>>>>>>> our system may use SQL to talk to the database. Using raw SQL also
>>>>>>> presents the disadvantage that, if one is not very careful in
>>>>>>> escaping
>>>>>>> variables, one may introduce SQL Injections vulnerabilities. We do
>>>>>>> not
>>>>>>> have to worry about that with the DAL.
>>>>>> I do understand the abstraction.
>>>>>> I worked with a product called DAL [1] for Mac OS Classic in the 
>>>>>> early
>>>>>> 1990's  (and others pre ODBC, which arrived in 1992 as Windows 
>>>>>> port of
>>>>>> what was then the SAG CLI) :-)
>>>>>>> The RDF tagging is done at the DAL level:
>>>>>>>  db.person.name.rdf = { .... }
>>>>>>> Anyway, it is possible there is some feature of ODBC that we have
>>>>>>> overlooked and we may be able to take  advantage of.
>>>>>> Yes.
>>>>>> You have ODBC itself. Then you have Virtuoso VDBMS (think scalable
>>>>>> high
>>>>>> performance variant of Microsoft Access JET Engine which major
>>>>>> benefits).
>>>>>> Kingsley
>>>>>>> Massimo
>>>>>>> On Dec 24, 2009, at 6:57 AM, Kingsley Idehen wrote:
>>>>>>>> Massimo Di Pierro wrote:
>>>>>>>>> Hello everybody,
>>>>>>>>> I am a new member of this list and first of all I wish everybody
>>>>>>>>> Happy
>>>>>>>>> Holidays.
>>>>>>>>> I also take the occasion to introduce the RDF plugin for web2py.
>>>>>>>>> http://web2py.com/semantic
>>>>>>>>> web2py is an Open Source web framework for rapid application
>>>>>>>>> development written in Python and programmable in Python. web2py
>>>>>>>>> runs
>>>>>>>>> almost everywhere and includes everything you need for web
>>>>>>>>> development
>>>>>>>>> in one package including a ssl-enabled web server, a
>>>>>>>>> transaction-safe
>>>>>>>>> relational database, a web-based IDE, a web-based database
>>>>>>>>> administration tool, and a Database Abstraction Layer that
>>>>>>>>> writes SQL
>>>>>>>>> for you and works transparently on SQLite, MySQL, Postgresql,
>>>>>>>>> Oracle,
>>>>>>>>> MSSQL, FireBird, DB2, Informix, Ingres, and on Google App Engine.
>>>>>>>>> Web2py requires no installation: just download, unzip and 
>>>>>>>>> click to
>>>>>>>>> start it.
>>>>>>>>> You can see an online demo here:
>>>>>>>>> http://web2py.com/demo_admin
>>>>>>>>> The RDF plugin allows to label (tag) database fields and 
>>>>>>>>> relations
>>>>>>>>> with ontologies and web2py automatically exposes the data in the
>>>>>>>>> database as Linked Data via a RESTful web service. Works with all
>>>>>>>>> database back-ends listed above.
>>>>>>>>> Any comment and feedback will be appreciated.
>>>>>>>> Any reason why you don't use ODBC for your data access? Your
>>>>>>>> references
>>>>>>>> above imply you implemented data access APIs on a DBMS by DBMS
>>>>>>>> basis.
>>>>>>>> ODBC is not only superior to all Native DBMS APIs, it is generic
>>>>>>>> thereby
>>>>>>>> shrinking you development and maintenance costs.
>>>>>>>> Kingsley
>>>>>>>>> Massimo
>>>>>>>>> -------------------------------------------------------
>>>>>>>>> Massimo Di Pierro
>>>>>>>>> Associate Professor
>>>>>>>>> School of Computing and Digital Media
>>>>>>>>> DePaul University
>>>>>>>>> 243 S Wabash Ave
>>>>>>>>> Chicago IL 60604
>>>>>>>>> +1-312-375-6536 (phone)
>>>>>>>>> +1-312-375-6116 (fax)
>>>>>>>> -- 
>>>>>>>> Regards,
>>>>>>>> Kingsley Idehen          Weblog:
>>>>>>>> http://www.openlinksw.com/blog/~kidehen
>>>>>>>> President & CEO
>>>>>>>> OpenLink Software     Web: http://www.openlinksw.com
>>>>>> -- 
>>>>>> Regards,
>>>>>> Kingsley Idehen          Weblog:
>>>>>> http://www.openlinksw.com/blog/~kidehen
>>>>>> President & CEO
>>>>>> OpenLink Software     Web: http://www.openlinksw.com
>>>> -- 
>>>> Regards,
>>>> Kingsley Idehen       Weblog: http://www.openlinksw.com/blog/~kidehen
>>>> President & CEO
>>>> OpenLink Software     Web: http://www.openlinksw.com
>> -- 
>> Regards,
>> Kingsley Idehen       Weblog: http://www.openlinksw.com/blog/~kidehen
>> President & CEO
>> OpenLink Software     Web: http://www.openlinksw.com



Kingsley Idehen	      Weblog: http://www.openlinksw.com/blog/~kidehen
President & CEO 
OpenLink Software     Web: http://www.openlinksw.com
Received on Thursday, 24 December 2009 18:51:34 UTC

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