TAG Action-354 Review client-side storage API’s

TAG Action-354 Review client-side storage API’s 

Introduction 

Originally there was a section in the HTML5 draft that specified a client-side database interface. This was split out into a separate draft. It has now morphed into two drafts, quite different in style and capability under the aegis of the Web Apps WG. [1],[2] 

The requirements for client-side storage are not very crisp [3]. In addition to cookies on steroids, the following requirements seem reasonable: 

· Off-line accessible: Client storage should be accessible by a client-side web application even when the client cannot contact the server from which the data was loaded. 

· Secure: Client-side web applications are identified by the URL they were loaded from. A client side web application is only able to access storage associating with a matching domain and path. (Like cookies.) 

· Controlled transmittal: Unlike cookies, local storage need not be transmitted to the server on each HTTP request. Instead applications can send *selected* client data to the server under program control. 

Web SQL Database [1] 

Web SQL Database presents a SQL-like interface for storing and retrieving client-side data. I say SQL-like because it is not SQL or even a subset of the SQL standard. It is based on a specific product called SQLite – the text says “ User agents must implement the SQL dialect supported by Sqlite 3.6.19.” It seems curious to write a standard based on specific software product . An argument has also been made that multiple uses of SQLlite by vendors do not constitute independent implementations. 

In point of fact, SQLite does not support a “dialect of SQL”, it is fundamentally different in a significant way: it supports weak, dynamic typing rather than SQLs strong static typing. 

Another question worth asking is whether the functionality of SQL is needed for a facility to store and retrieve name-value pairs. Even if the browser vendors don’t have to implement the function it does bloat the linked libraries. 

In response to arguments such as the above and others See [4],[5], an alternate client-side storage specification called Indexed Database API has been developed. On the other hand, a couple of browser vendors claim to have implemented Web SQL Database [6],[7]. Note that Google Gears uses SQLite. 

Indexed Database API [2] 

This used to be called WebSimpleDatabase but the new name seems better as it reflects the capabilities which offer indexed storage for name-value pairs. Databases can be created to store sets of key-value pairs. The value can be an object with properties. Indexes can be created on any of the value properties for efficient retrieval. A key-value record is retrieved by making an API call that either iterates over a range of keys in the object store or by identifying the key corresponding to the required record. 

Status 

Both WebSQLDatabase and Indexed Database API are at WD stage . Philippe requested an analysis for the various storage APIs. A Wiki with analysis is at [8]. 

Bottom Line 

It would be unwise to have more than one standard for client-side storage. There seems to be a technical preference for Indexed Database API over WebSQLDatabase but some vendors have implemented WebSQLDatabase and are getting ready to ship. See [9]. The Indexed Database API is referred to by the first name of the author: Nikunj. 

Meanwhile, Ian Hickson has asked for the WebSQLDatabase spec to be taken to Last Call [10]. There is, however, a subsequent thread on “parking” WebSQLDatabase by publishing it as a WG Note [11]. 


[1] http://dev.w3.org/html5/webdatabase/ 
[ 2] http://dev.w3.org/2006/webapi/WebSimpleDB/ [3] http://lists.w3.org/Archives/Public/public-webapps/2009AprJun/0303.html [4] http://www.w3.org/mid/63df84f0909011636x6ce5327ds241032a3b7080fe1@mail.gmail.com 
[5] http://www.w3.org/mid/C84F9222BE3A34439A7F58655086DFD70CD9896DE0@AA-EXMSG-C426.southpacific.corp.microsoft.com 
[6] http://webkit.org/blog/126/webkit-does-html5-client-side-database-storage/ 
[7] http://lists.w3.org/Archives/Member/chairs/2009JulSep/0046.html 
[8 ] http://www.w3.org/2008/webapps/wiki/Database 
[9] http://www.w3.org/2009/11/02-webapps-minutes.html#item11 
[10] http://lists.w3.org/Archives/Public/public-webapps/2009OctDec/1121.html 
[11] http://lists.w3.org/Archives/Public/public-webapps/2009OctDec/0526.html 

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All the best, Ashok