| ---+ Type System |
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| ---++ Introduction |
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| ---++ Overview |
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| ---+++ Data Types Overview |
| <img src="images/twiki/data-types.png" height="400" width="600" /> |
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| ---+++ Types Instances Overview |
| <img src="images/twiki/types-instances.png" height="400" width="600" /> |
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| ---++ Details |
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| ### Structs are like C structs - they don't have an identity |
| - no independent lifecycle |
| - like a bag of properties |
| - like in hive, also |
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| ### Classes are classes |
| - like any OO class |
| - have identity |
| - can have inheritence |
| - can contain structs |
| - don't necessarily need to use a struct inside the class to define props |
| - can also define props using AttributeDefinition using the basic data types |
| - classes are immutable once created |
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| ### On search interface: |
| - can search for all instances of a class |
| - classes could become tables in a relational system, for instance |
| - also databases, columns, etc. |
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| ### Traits is similar to scala - traits more like decorators (?) |
| - traits get applied to instances - not classes |
| - this satisfies the classification mechanism (ish) |
| - can have a class instance have any number of traits |
| - e.g. security clearance - any Person class could have it; so we add it as a mixin to the Person class |
| - security clearance trait has a level attribute |
| - traits are labels |
| - each label can have its own attribute |
| - reason for doing this is: |
| - modeled security clearance trait |
| - want to prescribe it to other things, too |
| - can now search for anything that has security clearance level = 1, for instance |
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| ### On Instances: |
| - class, trait, struct all have bags of attributes |
| - can get name of type associated with attribute |
| - can get or set the attribute in that bag for each instance |
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| ### On Classification: |
| - create column as a class |
| - create a trait to classify as "PHI" |
| - would create the instance of the column with the PHI trait |
| - apply traits to instances |
| - CAN'T apply traits to class |
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| ### Other useful information |
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| HierarchicalClassType - base type for ClassType and TraitType |
| Instances created from Definitions |
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| Every instance is referenceable - i.e. something can point to it in the graph db |
| MetadataService may not be used longterm - it is currently used for bootstrapping the repo & type system |
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| Id class - represents the Id of an instance |
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| When the web service receives an object graph, the ObjectGraphWalker is used to update things |
| - DiscoverInstances is used to discover the instances in the object graph received by the web service |
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| MapIds assigns new ids to the discovered instances in the object graph |
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| Anything under the storage package is not part of the public interface |
