Massimo Di Pierro wrote:
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.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."
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 ?
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 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."
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).We could use pyODBC on Oracle as we do with with DB2 but the installation process would be more cumbersome.
Post installation we even give you basic connection exercisers or a platform port of the ODBC Driver Manager that verifies DSNs post creation.
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?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.
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.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.
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 smallpart 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:passw...@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 highperformance variant of Microsoft Access JET Engine which major benefits).KingsleyMassimo On Dec 24, 2009, at 6:57 AM, Kingsley Idehen wrote:Massimo Di Pierro wrote:Any reason why you don't use ODBC for your data access? Your referencesHello everybody,I am a new member of this list and first of all I wish everybody HappyHolidays. 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 runsalmost everywhere and includes everything you need for web developmentin 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.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 therebyshrinking you development and maintenance costs. KingsleyMassimo ------------------------------------------------------- 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/~kidehenPresident & 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/~kidehenPresident & CEO OpenLink Software Web: http://www.openlinksw.com
