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Re: Web Storage & SQL

From: Kris Zyp <kris@sitepen.com>
Date: Wed, 08 Apr 2009 16:17:33 -0600
Message-ID: <49DD227D.5080503@sitepen.com>
To: Vladimir Vukicevic <vladimir@mozilla.com>
CC: public-webapps@w3c.org
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Vladimir Vukicevic wrote:
> (I originally blogged this at
> http://blog.vlad1.com/2009/04/06/html5-web-storage-and-sql/, but
> Hixie rightfully pointed out that I should post it here for
> discussion -- doing so!  Blog post is copied pretty much verbatim
> below, so apologies if it sounds more blog-y than post-y.)
>
> There's been a lot of interest around the Web Storage spec
> (formerly part of whatwg HTML5), which exposes a SQL database to
> web applications to use for data storage, both for online and
> offline use.  It presents a simple API designed for executing SQL
> statements and reading result rows.  But there's an interesting
> problem with this; unlike the rest of the HtML5, this section
> defines a core piece of functionality in terms of an undefined
> chunk referenced as "SQL".
>
> The initial implementations of Web Storage are both based on
> SQLite, and expose the dialect of SQL understood by SQLite to web
> content. I'm actually a big fan of SQLite, and was one of the
> advocates for pulling it into the Gecko platform.  However, SQLite
> implements a variant of SQL, with a number of deviations from other
> SQL engines, especially in terms of the types of data that can be
> placed in columns.
>
> Web content that is created to use database storage with SQLite as
> the backing is unlikely to work with any other backend database.
> Similarly, if another database was chosen as a browser's backing
> implementation, web content that works with it is unlikely to work
> with anything else. This is a serious interop problem, the root of
> which is that there really isn't a useful core SQL standard.  SQL92
>  is generally taken as a base, but is often extended or altered by
> implementations.  Even beyond the parser issues (which could be
> resolved by defining a strict syntax to be used by Web Storage),
> the underlying implementation details will affect results.
>
> So, the only option is for the Web Storage portion of the spec to
> state "do what SQLite does".  This isn't specified in sufficient
> detail anywhere to be able to reimplement it from the documents, so
>  it would be even worse  "do what this exact version of SQLite
> does", because there are no guarantees that SQLite won't make any
> incompatible changes.  For example, a future SQLite 4 may introduce
>  some changes or some new syntax which wouldn't be supported by
> earlier versions.  Thus, it requires every single browser developer
>  to accept SQLite as part of their platform.  This may not be
> possible for any number of reasons, not the least of which is it
> essentially means that every web browser is on the hook for
> potential security issues within SQLite.
>
> Instead of all of this, I think it's worth stepping back and
> consider exactly what functionality web developers actually want.
> It's certainly much easier to say "well, server developers are used
>  to working with SQL, so let's just put SQL into the client", but
> it's certainly not ideal  most people working with SQL tend to end
>  up writing wrappers to map their database into a saner object API.
>
>
> So, I would propose stepping back from Web Storage as written and
> looking at the core pieces that we need to bring to web developers.
>  I believe that the solution needs to have a few characteristics.
> First, it should be able to handle large data sets efficiently; in
> particular, it should not require that the entire data set fit into
>  memory at one time.  Second, it should be able to execute queries
> over the entire dataset.  Finally, it should integrate well with
> the web, and in particular with JavaScript.
>
> With these needs in mind, I think there are other options that
> should be considered, even beyond a subset of SQL; for example, an
> object-oriented database approach might serve those needs better.
> A good prototype example of what such a system could look like is
> jLINQ, which implements client-side querying on JavaScript objects
> and arrays.  As such, a basic implementation is simple; more
> complex ones can have browser support for efficient indexing,
> triggers, rapid serialization to and deserialization from disk,
> etc.  An implementation could even map all of this on top of an
> underlying SQL engine.  Another option is something like CouchDB.
> I was also just pointed at Persevere, which looks quite cool; much
> in the same way as CouchDB, the same API could be implemented both
> client-side and server-side, for efficient online/offline
> switching.  An approach such as one of these could well serve the
> web better than just throwing a SQL dialect over the web content
> fence.
>
In Dojo, we are using JSONQuery query language, which is basically an
extended version of the popular JSONPath query/path format. So far, we
have very positive feedback from those in the community that are using
it. We opted for this instead of SQL because it is more much more
similar to JavaScript in it's syntax, well-adapted for JSON-esque
object-oriented data (trying to cram SQL on to objects is tough), it
can be easily used within URLs for server-side queries that maintain
the same syntax, and it is easier to secure than SQL on the server
(due to the complexity of SQL). Here is a post describing JSONQuery in
Dojo:
http://www.sitepen.com/blog/2008/07/16/jsonquery-data-querying-beyond-jsonpath/

We also use JSONQuery in Persevere (which you referenced). When using
Dojo and Persevere together this does indeed create a very pleasant
situation where the same query language can be used both client and
server side. In particular, it is possible for the client to use the
query language both locally (in the JS impl in Dojo) to query
client-side cached data and within URLs that query the server. Doing
that with SQL is asking for trouble.

I also recently created a mailing list for the discussion of this
query language with the hope of community development of this type of
object-oriented JavaScript-esque query language suitable for embedding
in URLs and easily implementable in JS as well as other languages:
http://groups.google.com/group/json-query
I hadn't really considered this query format for web storage, but
since Vladimir brought it up, I thought I would mention it.

Thanks,

- --
Kris Zyp
SitePen
(503) 806-1841
http://sitepen.com
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Received on Wednesday, 8 April 2009 22:19:15 GMT

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