I went through Sciore&#x27;s book [0] while learning about relational database internals. As part of his book, the author also developed a minimal database system named SimpleDB [1] in Java. I can safely say that its source code is very easy to understand. Though the book is not free, SimpleDB is.<p>[0]: <a href="http:&#x2F;&#x2F;eu.wiley.com&#x2F;WileyCDA&#x2F;WileyTitle&#x2F;productCd-EHEP000711.html" rel="nofollow">http:&#x2F;&#x2F;eu.wiley.com&#x2F;WileyCDA&#x2F;WileyTitle&#x2F;productCd-EHEP000711...</a><p>[1]: <a href="http:&#x2F;&#x2F;www.cs.bc.edu&#x2F;~sciore&#x2F;simpledb&#x2F;intro.html" rel="nofollow">http:&#x2F;&#x2F;www.cs.bc.edu&#x2F;~sciore&#x2F;simpledb&#x2F;intro.html</a>