block explorer, just a parser and database query?
Yeah, that's how they work. For example, blockexplorer.com gets blocks from Bitcoin Core via JSON-RPC, gathers interesting chunks of data, and puts this data into a SQL database for easy access later. The code for this is only ~300 lines long (though it's very messy). Other block explorers work similarly. In fact, Bitcoin Core itself works something like this, though it uses a key-value database instead of a relational database, and it doesn't store any info about addresses.