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copied!<p>Sharing data in the three ways you've out-lined (via Web Services) is indeed possible, but there's lots of other factors which will drive the right approach.</p> <p>Architectural aspects to consider:</p> <ul> <li>Data Architecture (business ownership, security, management and so on).</li> <li>Data quality - is it at an appropriate level for the consuming applications?</li> <li>How will you keep related data (in related systems) in sync?</li> <li>The case of use: Transactional (OLTP) vs Analytical (OLAP).</li> </ul> <p>Things to consider when integrating with another system:</p> <ul> <li>What's the case of use: Transactional (<a href="http://en.wikipedia.org/wiki/OLTP" rel="nofollow">OLTP</a>) or Analytical (<a href="http://en.wikipedia.org/wiki/OLAP" rel="nofollow">OLAP</a>)?</li> <li>How many requests are we talking about and when do they occur, etc?</li> <li>How complex are the queries likely to be that service these requests?</li> <li><strong>Exactly</strong> how up-to-date does the data need to be?</li> </ul> <p>If your data exists in a single DB that's serving a transactional system then any queries made against it can affect performance of that system; if you have many systems hitting that database then you've got a crucial piece of data infrastructure to protect - it goes down so does everything else.</p> <p>Databases written to support transactional systems often aren't suited to analytical ones. A common approach where I work is to ETL out copies of the data into a repository designed for the purpose in mind. The other advantage is that (as it's in a separate system) you won't get performance issues on either side.</p> <p>Assuming you do ETL out the data to a new repository which source is the authoritative one? It might be that several applications ETL data into a central <a href="http://en.wikipedia.org/wiki/Data_mart" rel="nofollow">Data Mart</a> or Data Warehouse where that data is integrated - and that becomes the "source of truth".</p> <p>In closing - working with data (both logically and physically) is a lot like Object Orientated programming / design: a lot of the underlying principles (like <a href="http://en.wikipedia.org/wiki/Solid_%28object-oriented_design%29" rel="nofollow">SOLID</a>) readily apply.</p>

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