Creating an Abstraction Layer in Software

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Creating an Abstraction Layer
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This allows your customer service employees to see the data they are meant to see In addition, what if you need to add a sensitive piece of information to a table that not everyone needs to see For example, suppose you need to start storing all your customers social security numbers; you add a new column to tbl_customer called SSN Any users who currently have read access to the table can now see this new SSN column, whether or not you want them to have that access Extra steps need to be taken to prevent them from seeing the new data But when you use an abstraction layer, this problem ceases to exist Adding a column to a table does not automatically add it to your view, provided you didn t create your view using the SELECT * syntax Now the extra steps would be required to expose the data, and not to hide it To expose the information, you would need to modify any views you want this new column to appear in, or create new views
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Extensibility and Flexibility
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Extensibility refers to the ease with which you can modify your data model as your future needs change By change, we mean adding columns to hold new pieces of information, modifying existing columns to change the way data is stored, or even adding or removing whole tables It s hard to predict what our future needs will be, so it is our job to make the database as extensible as possible so that we can react to future needs as they arise We also want our models to be flexible Although it s similar to extensibility, flexibility refers to how much of your model you can change without causing significant or any impact It is true that flexible models will likely also be extensible, but this isn t always the case In either event, an abstraction layer is your best friend when it comes to extensibility Your abstraction layer allows you to make almost any change you can imagine to the physical tables and not affect a single piece of application code If all your applications and users are reading data from views and manipulating data using stored procedures, you simply need to update these items as appropriate to prevent problems How many times have you wanted to make a change to a database, such as splitting one table into two tables, but have not been able to because it would require code to be reviewed, changed, and recompiled We have been in this boat more times than we care to remember The problem stems from the lack of an ab-
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An Abstraction Layer s Relationship to the Logical Model
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straction layer In the example of splitting one table (TableA) into two tables (TableA and TableB), any code that selects, inserts, updates, or deletes from TableA must be changed to perform its action on both tables If we have an abstraction layer, we need only modify a few stored procedures and views to accommodate the new structure You are probably thinking, Code will need to be modified either way, so what s the difference Although it is true that in either case you need to make a change, the difference is huge For starters, unlike code in a NET application, code on SQL Server is not compiled; therefore, if the procedure takes the same inputs and returns the same outputs, you can alter that procedure in the middle of the day while users are online and no one will know the difference Granted, there are other considerations based on what else you have to change in the database, but we are talking about the transparency of the stored procedure change The second, and probably the more important, difference in modifying stored procedure code over application code is that there is only one database If you change application code, you often need to recompile and then have all your users update or reinstall the client application Abstraction layers give you the flexibility to make changes for performance reasons, for normalization, and for reasons of extensibility Future growth and changes are always similar with an abstraction layer
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