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PODatabase design rules to follow for a programmer
 

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    <p>We are working on a mapping application that uses Google Maps API to display points on a map. All points are currently fetched from a MySQL database (holding some 5M + records). Currently all entities are stored in separate tables with attributes representing individual properties. </p> <p>This presents following problems:</p> <ol> <li><p>Every time there's a new property we have to make changes in the database, application code and the front-end. This is all fine but some properties have to be added for all entities so that's when it becomes a nightmare to go through 50+ different tables and add new properties.</p></li> <li><p>There's no way to find all entities which share any given property e.g. no way to find all schools/colleges or universities that have a geography dept (without querying schools,uni's and colleges separately).</p></li> <li><p>Removing a property is equally painful.</p></li> <li><p>No standards for defining properties in individual tables. Same property can exist with different name or data type in another table.</p></li> <li><p>No way to link or group points based on their properties (somehow related to point 2).</p></li> </ol> <p>We are thinking to redesign the whole database but without DBA's help and lack of professional DB design experience we are really struggling. </p> <p>Another problem we're facing with the new design is that there are lot of shared attributes/properties between entities.</p> <p>For example:</p> <p>An entity called "<strong>university</strong>" has 100+ attributes. Other entities (e.g. hospitals,banks,etc) share quite a few attributes with universities for example atm machines, parking, cafeteria etc etc.</p> <p>We dont really want to have properties in separate table [and then linking them back to entities w/ foreign keys] as it will require us adding/removing manually. Also generalizing properties will results in groups containing 50+ attributes. Not all records (i.e. entities) require those properties. </p> <p><em>So with keeping that in mind here's what we are thinking about the new design</em>:</p> <ul> <li><p>Have separate tables for each entity containing some basic info e.g. id,name,etc etc.</p></li> <li><p>Have 2 tables <strong>attribute type</strong> and <strong>attribute</strong> to store properties information.</p></li> <li><p>Link each <strong>entity</strong> (or a table if you like) to <strong>attribute</strong> using a many-to-many relation.</p></li> <li><p>Store addresses in different table called <strong>addresses</strong> link entities via foreign keys.</p></li> </ul> <p>We think this will allow us to be more flexible when adding, removing or querying on attributes.</p> <p>This design, however, will result in increased number of joins when fetching data e.g.to display all "<strong>attributes</strong>" for a given university we might have a query with 20+ joins to fetch all related attributes in a single row.</p> <p>We desperately need to know some opinions or possible flaws in this design approach.</p> <p>Thanks for your time.</p>
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