ExecutionEngine DataTypes

Overview

The two main execution pillars of the ExecutionEngine are invocations and data. This section covers the later. The ExecutionEngine supports a number of commonly used data types inherently and provides abstractions to cover all non primitive ones. These supported data types are covered in the following sections.

The direction followed by the ExecutionEngine aims to solve the following problem. In the context of a distributed environment that cannot afford to create a canonical data model perfectly defining the full range of transfered messages, there must be a way to describe the data moved without binding them to specific classes, packages or even schema. But still the way of capturing the data must contain enough information to be able to reconstruct the needed structures populating them with the stored values.

One way to go around this problem is to identify common workflow patterns, in an offline fashion, so that data exchange directions and pairs can be identified. Then, transformation utilities could be defined to support the identified pairings. These of course could explode to an unmanageable size of such transformations while it might only be applicable (keeping a curtain level of generality) to Web Service invocations, while POJO based transformations might become much more intrusive to client code.

This approach was not the one pursued by the ExecutionEngine and the underlying data types approach detailed in this section. The approach taken was that of non intrusive description of types and collection of types based on a wide list of primitives that are inherently manageable by the engine. These primitives are listed in following sections. This way, a component that needs to be invoked with some parameters or returns some parameter that needs to be later used, needs only to have a way of describing the structure and type of its type with respect to the engine constructs. After this mapping is performed, the engine can then provide a number of generic manipulation utilities that can process and transform the stored types to any type that is needed by the rest of its clients. For many of the listed constructs, even that specific mapping is not needed as the engine does its best to retroactively sketch all the needed information at runtime. Of course there may be cases where a needed type may not be easily mapped to the supported constructs. In that case there are still utilities offered to cover all needs even if that would require a more tight client binding.

Supported data types

• BooleanClass

  A boolean object type (java.lang.Boolean)

• BooleanPrimitive

  A boolean primitive type (boolean)

• DoubleClass

  A double object type (java.lang.Double)

• DoublePrimitive

  A double primitive type (double)

• FloatClass

  A float object type (java.lang.Float)

• FloatPrimitive

  A float primitive type (float)

• IntegerClass

  An integer object type (java.lang.Integer)

• IntegerPrimitive

  An integer primitive type (int)

• String

  A String object type (java.lang.String)

• ResultSet

  An IProxyLocator type capable of identifying a result set

• RecordStore

  An IStoreLocator type capable of identifying a result set that is stored in some record store

• Convertable

  A type capable of storing information on a type that is not directly supported but can be transformed into a string serialization from an object and then back into the object using some converter object

• Reflectable

  A type capable of storing information on named data types that can be used to populate or be populated from an object that follows the generic get/set pattern on member variables of the respective names

• Array

  A multidimensional array of one of the above types

Highlights

• Wrapped and unwrapped types

  The reason of having for primitive types also the wrapped version of them (Integer primitive and integer Class), is mainly due to Java's reflection API and the way these Java types are distinguished from one another. So should for example part of the execution plan needs to make a call to some Java object's method through reflection, then the exact type as defined in the signature of that method must be available. If the method's signature requires an int and it is provided with an Integer, an error will occur.

• Convertables

  This Data Type category provides the biggest flexibility concerning the value that can be passed to an element invoked by the ExecutionEngine or returned to it by an invocation when the involved invokable is a POJO. But this also comes with the toll of having to produce the respective Converter utility for each object that will be passed back to the ExecutionEngine or be delivered by it. And this Converter utility will have to implement an interface that is defined by the ExecutionEngine library meaning that the portability of the package is hurt. Even so, the capability is offered in cases where portability is not of great importance.

• Refelctables

  This Data Type category provides the largest generality without binding the client implementation to any execution engine libraries. As most of the types passed as arguments or are returned as results mainly act as containers of other primitive types, this utility offers the possibility of abstracting over these objects through the means of the regularly used get/set methods. An object returned by a client class invocation is scanned through reflection and the getters and setters found dictate the member values it offers. These values are then extracted through the respective getter method and are stored under the name that joins the get and set method (e.g. for int getX() and setX(int x), the common name is X). Respectively when populating an argument, the getters and setters are retrieved and wherever the common name matches one of the names available through the reflectable data type as well as the type, the setter is used to set the payload needed. This scanning can work recursively to sketch a very deep level of encapsulation. This Data Type in conjunction with the Array data type can cover most of the foreseen common usage scenarios.

Usage

The following snippets demonstrate the definition of some of the above listed data types.

IDataType dt1=new DataTypeBooleanPrimitive();
dt1.SetValue(true);

<dt type="BooleanPrimitive"><value>true</value></dt>

IDataType dt2=new DataTypeString();
dt2.SetValue("Hello World of D4Science");

IDataType dt3=new DataTypeConvertable();

((DataTypeConvertable)dt3).SetConverter(ObjectImplementingIObjectConverter.class.getName());

IDataType dt4=new DataTypeArray();
((DataTypeArray)dt4.Value).SetArrayClassCode("["+IDataType.DataTypes.IntegerPrimitive);
((DataTypeArray)dt4.Value).SetValue(new int[] {1,2,3,4,5});