DBLP for SQL Server

March 27, 2011 — naiem

DBLP is the mainstream computer science publication database. Everybody can download its dataset from here for free.  It is a good benchmark dataset for many algorithmic research purposes. For example if you work on an entity resolution algorithm, you can benchmark it against this dataset which includes numerous data quality issues.

I have used this data set multiple times for my own work, however, for someone like me which uses a commercial RDBMS, a little bit of work is required to utilise this dataset. The original dataset which you can download from the above link is an XML file suitable for a column store database (link MonetDB). However, most commercial DBMS are table store and you should find a way to make this xml suitable for your DBMS.

Although it is not particularly hard to implement and takes only a few hours to figure out what to do and less than an hour to implement it, I put my solution HERE which may save you a few hours.

It basically converts dblp’s cml to flat csv’s that you can import to your DBMS. A copy of SQL Server 2008 R2 backup file is also included in the solution for your convenience.

(Update: Sorry I removed the SQL Server backup file because it was slowing down the checkout)

To use the code, you should first check out the code from the project folder (using svn). There is a project called Dblp_xml2csv, which is a Console Application. Set this project as the startup project and run the Console App.

You need to have downloaded DBLP dataset in the xml format. Go to where dblp_xml2csv.exe is built and run the following command:
>dblp_xml2csv.exe dblp-data.xml

You can replace dblp-data.xml with the path of the dblp xml file.

There is no need for the companion xsd, because for performance reasons Xml dataset is treated as a text file.

Running the above command will create a couple of .csv files. You can use the csv file to import to SQL server or Excel, etc.

Additional stuff in the solution are related to some work I was doing on a DQ estimation technique and would not be much helpful to you probably.

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Posted in Computer Science, Data Quality, SQL Server. 5 Comments »

View Matching

March 12, 2011 — naiem

View Matching is a fairly old technique first seriously utilised at the beginning of the millennium. Lars et al from Microsoft research exploited this technique for SQL Server 2000.

The idea is to utilise existing materialised views (or indexed views in SQL Server) for query optimisations. For example, if you query “SELECT * FROM Cars WHERE Brand=’BMW’ and PRICE BETWEEN 40,000 AND 70,000” and there is already an indexed views over the cars called v_LuxuryCars which is defined as “SELECT * FROM Cars WHERE PRICE > 40,000”, the query optimiser can exploit v_LuxuryCars for executing the query. This view can be much smaller than the base table and the query can run faster. The real beauty of exploiting materialised views will be obvious in more complex queries though.

The challenge here is how to efficiently figure out if a view can be used for the query. Indeed, if the query predicate, is a subset of the view definition predicate (like the given example; PRICE BETWEEN 40k AND 80K is a subset of PRICE > 40K). This is not straight forward since the predicates can be really complicated. For example query may have the predicate A=2 and B=2, while the view definition has the predicate A=B. In that case the inference of the predicate sub/super relationship is  not obvious).

However, this problem is well studied for relational algebra and even though Microsoft have been very active in developing View Matching techniques, it is not used in the SQL Server core, possibly for performance reasons.

The reason I am interested in view matching is that I have started a project for View Matching over IQueriable interface. I will keep you posted about the progress.

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