Collections create collection Contacts : set of contact

Avon Implementation

Overview

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Avon Interfaces

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Avon Model

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Avon Storage

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Avon Query Processor

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Demo

Avon Interfaces

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Programmatic Interface: OMSjp 1.2

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OML (last week)

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Graphical Interfaces

ƒ Eclipse Plugin

ƒ OMSjp Browser (DEMO)

Programmatic Interface

Programmatic Interface: OMSjp

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Java interface to OM model

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Support for multiple inheritance, classification, role modeling, query, data definition and

manipulation

Architecture

ƒ Client-Server

ƒ Multiple clients

Java Virtual Machine

Database Application

OMSjp

OMS Platform OMSjp Interface

Driver(s) Cache Java Virtual Machine

Database Application

OMSjp

OMS Platform OMSjp Interface

Driver(s) Cache

ƒ Inprocess

ƒ Personal mobile information systems

OMS Driver

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Abstraction from underlying OM Implementation

ƒ One per platform

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DriverManager

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Driver configuration via URL

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Similar to JDBC

<omsjp:platform:user/password@host:port/database>

<omsjp:avon:stefania/***@localhost/test.oms>

Mapping OM to Java

ƒ A person can be both, student and employee

ƒ Multiple Instantiation

ƒ Impedance mismatch with Java

person

student phd student employee

Mapping OM to Java…

Metamodel of OM Object

Most Important Classes

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OMSObject

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OMSObjectType

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OMSInstance

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OMSCollection

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OMSAssociation

Example: Type Schema

create type contact (…);

create type person subtype of contact ();

create type location (…);

create type organisation subtype of contact (…);

…

contact

person organisation

location

Example: Classification Schema

contact

Contacts

person

Persons

organisation

Organisations

cover

location

Locations located_at

(0:*) (0:*)

lives_at (1:*)

(0:*)

// Collections

create collection Contacts : set of contact;

create collection Persons : set of person;

create collection Organisations : set of organisation;

…

OMSObject

ƒ dress(ObjectType type), strip(ObjectType type)

ƒ setAttributeValue(…), getAttributeValue(…)

//create john object and set attribute values

final OMSObjectType contactType = database.getObjectType(“contact");

final OMSObject john = database.createObject(contactType);

john.setAttributeValue(contactType, “name", "John");

…

//dress john as person john.dress(personType);

john.setAttributeValue(personType, “birthDate", "20.12.1978");

OMSObject…

ƒ getMembershipCollections(), getMembershipCollections(Type type)

ƒ getLink(OMSAssociation assoc) and inverse

//get johns locations

final List<OMSObject> locations = john.getLinks(locatedAtAssoc) //get johns homeplaces

final List<OMSObject> homeplaces = john.getLinks(livesAtAssoc) //get membership collections

final List<OMSCollection> colls = john.getMembershipCollections()

homeplaces locations

OMSObject and OMSInstance

final Person johnPerson = (Person)john.browse(personType);

String birthDate = johnPerson.getBirthDate();

final Contact johnContact = (Contact)john.browse(contactType) johnContact.setName(“Johnny”);

ƒ getInstances(), getDressTypes()

ƒ browse(ObjectType type)

OMSInstance: Contact Class

public class Contact extends AbstractInstance {

public void setName(final String name) throws OMSException { this.setAttributeValue(“name", name);

}

public String getName() throws OMSException {

OMSString s = (OMSString) this.getAttributeValue(“name");

return s.getString();

} ...

}

Instance registration: Mapping of Java classes to database types contact=ch.ethz.globis.test.Contact

How to implement the OMSjp classes?

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Create data

objects, types, collections, hierarchies, constraints

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Access data

getAttributeValue(…): …

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Manipulate data

setAttributeValue(…)

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^Processing

executeMethod(…): …

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Collections

add, retrieve, remove members, hierarchies, constraints

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^…

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… and Persistent

Model and Metamodel

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OMSjp interfaces represent metamodel concepts

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Interface implementation implements a metamodel

object Objects

type Types

collection Collections

association Associations disjoint

Example: A Simple Metamodel

We need to store and retrieve data

ƒ attributes declared by types

ƒ attribute values of objects

ƒ collection membership

ƒ …

Example: A Simple Metamodel …

ƒ Where is it stored that personType has a name and attributes?

personType is an instance of type with name = “personType” and declaring the attributes “name” of type string and “birthdate” of type date

ƒ Where is it stored that type has a name and attributes?

type is an instance of type with name = “type” and declaring the

attributes “name” of type string and “attributes” of type list<attribute>

Example: A Simple Metamodel …

ƒ What is an attribute?

attribute is an instance of type with name = “attribute” and declaring the attributes “name” of type string and “type” of type type

ƒ (OMSjp Metamodel: What is a collection?

collection is an instance of type with name = “collection” and declaring the attributes “name” of type string and “extent” of type bulktype

ƒ … method, association, hierarchy, constraint?)

Example: A Simple Metamodel …

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What Java classes can we use to represent

person objects, person types, types, attributes?

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What is common to all these objects?

They are all objects which store values for the attributes declared by their types

final Object personType = new Object();

personType.dress(TYPE);

personType.setAttributeValue(TYPE, nameAttribute, “person");

personType.setAttributeValue(TYPE, attributesAttribute, …);

final Object person = new Object();

person.dress(personType);

person.setAttributeValue(personType, nameAttribute, “daniel");

…

A Vicious Circle

final Object type = new Object();

type.dress(type);

type.setAttributeValue(type, nameAttribute, “type");

final Object nameAttribute = new Object();

nameAttribute.dress(attribute);

final Object attribute = new Object();

attribute.dress(type);

• Type has not declared its attributes

• Name attribute does not exist

• Attribute type does not exist

• Type has not declared its attributes

• Name attribute has not been initialised

ƒ When creating the type type we want to set its attributes “name” and

“attributes”.

ƒ We need the objects representing the “name” and “attributes” attributes

ƒ When creating the “name” attribute we must have the object representing the attribute type

ƒ When creating the attribute type we must have the object representing the type type (… but this is the one we were about to create)

// create types

final Object object = new Object();

final Object type = new Object();

…

// create attributes

final Object typeName = new Object();

final Object typeAttributes = new Object();

…

// dress

object.dress(object);

object.dress(type);

type.dress(object);

…

// create attribute values

…

// set type attributes values

object.setAttributeValue(type, typeName, objectNameValue);

object.setAttributeValue(type, typeAttributes, objectAttributesValue);

type.setAttributeValue(type, typeName, typeNameValue);

…

// set attributes attribute values

typeName.setAttributeValue(attribute, attributeName, typeNameName);

typeName.setAttributeValue(attribute, attributeType, typeNameType);

typeAttributes.setAttributeValue(attribute, attributeName, typeAttributesName);

…

Bootstrap

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Kind of pipelining to break out of vicious circle

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Objects created during bootstrap must be available to user

Avon Metamodel: Object Types

Avon Metamodel: Object Types …

name: String Collection

extent: Ranking<? ext Value>

RankingCollection

extent: Set<? ext Value>

SetCollection

extent: Bag<? ext Value>

BagCollection

extent: Sequence<? ext Value>

SequenceCollection

Avon Metamodel: Collections

Avon Metamodel: Types and Collections

(0:1)

(0:*)

type

Types

collection

Collections

method

Methods

objectType

ObjectTypes

type

BaseTypes

bulkType

BulkTypes

structuredType

StructuredTypes

partition

ObjectTypeISAs (0:*) (0:*)

BaseTypeISAs (0:*) (0:*) CollectionISAs

(0:*) (0:*)

HasMethods (1:1)

Extent (0:*)

Java Classes of Avon

initialise() Database CoreBootstrap BaseTypesBootstrap CollectionsBootstrap BootstrapManager

Java Classes of Avon …

Simplification the creation, retrieval and deletion of OMObject objects that represent the various

metamodel concepts

e.g. CollectionGateway.create(): OMObject

returns OMObject with types object and collection

Java Classes of Avon …

Simplification of setting and retrieving attribute values of OMObject objects

e.g. AttributeUtils.getName(OMObject): String

if argument is of type attribute, return its name AttributeUtils AssociationUtils

CollectionUtils

TypeUtils

ValueUtils Database

Utils

isAttribute(OMStructuredValue): boolean getName(OMObject): String

setName(OMObject, String) getType(OMObject): OMObject

AttributeUtils

isAssociation(OMObject): boolean getName(OMObject): String setName(OMObject, String)

getDomainCardinality(OMObject): OMStructuredValue getRangeCardinality(OMObject): OMStructuredValue getDomainCollection(OMObject): OMObject getRangeCollection(OMObject): OMObject getRelationCollection(OMObject): OMObject

AssociationUtils

Java Classes of Avon: Layering

Persistency Object Model

OMSjp

OMObject Database

Utils

Gateway

DBObject InformationUnit AttributeValue StorageBase

Utils

AvonObject AvonInstance AvonValue

AvonAssociation AvonCollection

AvonType

AvonSchema AvonDatabase

OML

Query

db4o

Storage Layer

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Uses db4o

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A new impedance mismatch between OM and java

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Object activation

Storage Layer

Storage Layer - DBObject

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Corresponds to OMObject from the OM layer

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Contains references to information units (an information unit for each type)‏

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^Dress adds information units

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^Strip removes information units

Storage Layer - DBObject

Type : Object

Object

Type : Object

Object

Type : Student Type : Person

Type : Object

Object

Type : Student Type : Person Type : Object

Object

Type : PhDStudent Type : Person

dress (Object, Student)‏

createObject

strip (Object, Student)‏

dress (Object, PhDStudent)‏

Storage Layer - CompositeValue

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Base class for StructuredValue and InformationUnit

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Type (object type or structured type)‏

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Values – associated with attributes of the type

Storage Layer - Activation

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Db4o activation - process of populating the

attributes of an object with previously stored data

container.activate (obj, 1)

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Transparent activation

Query Engine

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Language process with in a three level architecture.

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Extensions

Query Engine

Parser process

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JavaCC package used to generate parser and lexer.

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Returns an AST (abstract syntax tree)‏

QueryTree converter

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Transforms the AST into a QT (query tree)‏

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Uses the Visitor design pattern

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Postorder AST processing

Query Tree

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QT nodes are atomic construct that are used to build different database operations (Selection, Domain, Iterator, Object)‏

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A Visitor interface is associated with the tree structure

Query Tree

SituatedAt rr (all $l in Locations having

($l.city = "Zurich"))

Query Tree Evaluator

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Uses the Visitor interface of the QT

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Postorder traversal

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Returns only the last result from the OML script

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Memorizes the result in the node structure

Symbol Table

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Stores temporary object references

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Organized as a stack.

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Duplicate names in different scopes are allowed

Queries - storage layer

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OM queries are transform into SODA queries

ƒ sel (Locations, city, “Zurich”)‏

ƒ query.constrain (StringValue.class)

query. descend(“value”).constrain (“Zurich”) resStrVal = query.execute();

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Temporary query results are stored in db4o

Extensions

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Allow OML to grow

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Syntax expanders nodes (AST)‏

ƒ set[ `obj1.version(1.2)`, `obj2.version(1.0)`];

ƒ `grant R to UserName`;

Extensions

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An Extension Node is currently generated in the core AST.

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A separate module processes extension

strings ( `obj1.version(1.2)`, `obj2.version(1.0)`, ...)

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The extension module will return an AST

DEMO