The purpose of this document is to define the structure of OpenMDM® 5 components and their relationship with the OpenMDM® 5 Data Access module containing the MDM API and business object model.
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2. Introduction
The OpenMDM® 5 Architecture describes the composition of the OpenMDM® platform in terms of core services and components. Core services deliver the runtime facilities required by components to be instantiated, queried, and managed. Components define their behavior by specification; this allows vendors to provide different implementations as needed while making sure their implementations conform to a common set of APIs.
The architecture is defined in 4 layers, each one influencing the next:
- Goals
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A List of desired behavior and constraints that guide the design.
- Design
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An overview of the different moving parts in terms of elements and their relationships.
- Technologies
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Software standards and design patterns that can fulfil the requirements set for by the design.
- Products
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Libraries, frameworks and implementations that make use of the chosen technologies.
2.1. Conventions and Terms
2.1.1. Typography
A fixed width, non-serif typeface (sample) indicates the term is a Java package, class, interface, or member name. Text written in this typeface is always related to coding.
Emphasis (sample) is used the first time an important concept is introduced. Its explanation usually follows directly after the introduction.
2.1.2. Key Words
This specification consistently uses the words may, should, and must. Their meaning is well-defined in [1] Bradner, S., Key words for use in RFCs to Indicate Requirement Levels. A summary follows.
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must – An absolute requirement. Both the Framework implementation and bundles have obligations that are required to be fulfilled to conform to this specification.
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should – Recommended. It is strongly recommended to follow the description, but reasons may exist to deviate from this recommendation.
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may or can – Optional. Implementations must still be interoperable when these items are not implemented.
3. Driving Forces
Members of the OpenMDM® Working Group have identified the following driving forces that heavily influence the architecture goals and its design:
ASAM ODS is the selected technology for persistent storage and retrieval of testing data; it’s the key concern for OpenMDM® members as it enables them to share data using a standard format that’s not specific to a single member or vendor.
CORBA has proved to be a problem in previous iterations of the OpenMDM® API, most notably perhaps the fact that setting a CORBA broker is troublesome and error prone. Also, the CORBA API has leaked to the front all the way from the bottom layers.
It should be possible to read and write data from and to different proprietary formats and feed it into the OpenMDM® Data Acess module.
Members of the OpenMDM® Working Group already posses large amounts of data stored in the OpenMDM® 4 format. This data should be able to be consumed in read-only mode. Any changes made to data in this format should be written back in the OpenMDM® 5 format.
There are many existing components OpenMDM® 4 already but none of them must be used as a basis for design and implementation. In other words, the OpenMDM® 5 components should be designed from scratch, however reuse of previous knowledge is highly desired.
4. Goals
The following goals have been identified by the OpenMDM® Working Group as must have.
4.1. Modularity
Modularity boils down to the ability to interchange component implementations while keeping a base level of behavior.
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Ability to replace any component with another one that performs similar behavior.
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Should be able to distribute work to different providers and independently from each other.
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Strict separation of interfaces vs. implementation.
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Each module has a defined place in the architecture layers. Must not access upper layers.
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Only dependencies on interfaces.
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UI layer should allow modularity.
4.2. Assembly
OpenMDM® 5 applications should be built as a composition of OpenMDM® 5 components. It’s desired by some OpenMDM® Working Group members that this composition happens using a declarative approach, using only configuration and no additional code involved.
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Capability to aggregate components by configuration.
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Components expose metadata about their compatibility and UI capabilities.
4.3. UI Independence
OpenMDM® 5 components should be able to be assembled into OpenMDM® applications that have different UI technology stacks from one another. This enables a component to be reused on a Rich Client and Web stacks for example.
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Components should provide hooks for different UI technologies to be used.
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Don’t force a single UI technology unless that’s what the component’s behavior demands.
4.4. Conformance to Specification
OpenMDM® 5 components should define their inputs/outputs and operations using a well known definition language. This is will be known as the OpenMDM® 5 Component Specification.
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Components must be certified through an OpenMDM® TCK.
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Components must comply with a CTCK that arises from the component’s specification.
OpenMDM® 5 Component Specifications will be validated and tested using a particular OpenMDM® 5 CTCK.
4.5. Resilience
Components can be exchanged while the system (not an application) is running. This accommodates for fail-overs, load balancing and scalability. Connections between components and their communication protocols should be elastic and flexible, that is, if a component is taken offline and replaced immediately other parts of the system may work without having to take them down, too.
5. Overview
The following figure shows a basic view of three OpenMDM® 5 applications connected to the OpenMDM® Data Access module. The OpenMDM® Data Access module is responsible for transforming data from and to ASAM ODS, as well as executing specific MDM operations on said data. The components are responsible for building new behavior on top of the OpenMDM® Data Access module, such as custom searches, archiving, security. Notice that all three applications share a common component (the blue one).
Interestingly, these three applications use different UI technologies however they are able to share some components. This is possible because components can be designed in such a way that their core behavior and inputs/outputs can be defined independently of a specific UI technology. We propose the usage of the Remote Presentation Model pattern to fulfil this design goal.
The Presentation Model pattern as explained by Martin Fowler can be further extended to work under networking conditions, such that there are two halves of a Model: one at the client side, the other at the server side. Setting a value on one side transfer it to the other and vice versa. Value transfer can happen synchronously (set and wait) or asynchronously (set and continue). We prefer the latter mode as synchronization points (if needed) can be built on top of an asynchronous system, whereas the reverse is much more difficult to achieve.
Once a Remote Presentation Model is in place it enables developers to push the logic to the server side. This frees developers from reimplementing application logic for each different UI stack that’s chosen. Building a new client using a different UI technology results in more reusability as it’s only the new visuals that must be created, as the logic and data interactions remains the same. The Presentation Model pattern also fosters code reusability and increased decoupling of View components from Controllers (or Logic) components.
It’s worth mentioning that command line applications may not require the Presentation Model approach (though they can benefit from it too). This is because an OpenMDM® Component can expose its data and behavior with multiple channels. These channels will be explained in the next section.
5.1. Anatomy of an OpenMDM® Component
There are two types of OpenMDM® 5 components: Rich and Headless. This distinction is made solely on the terms of UI capabilities that the component may expose. Rich components deliver at least one UI part. These are the type of components that require the usage of the Remote Presentation Model pattern. On the other hand, Headless components do not expose an UI part and therefore are not required to use a Remote Presentation Model. The following figures depict both types of components
OpenMDM® components may expose their input/outputs and operations using the following channels:
Used by OpenMDM® components co-located within the same JVM process; think of instances accessed via dependency injection.
Used exclusively by UI clients that support the Remote Presentation Model pattern. This channel must be used to build up Rich and Web clients.
Used by clients that require offline capabilities and/or those that do not support the Remote Presentation Model pattern.
Used by OpenMDM® components that are located in different JVM processes. This channel is the preferred way of communicating two components over a well-known business (e.g, behavior) interface.
Used by any OpenMDM® component, whether local or remote; his enables low coupling of components and broadcasting of data. This channel enables one component to communicate with multiple components without any single component having a direct reference to the others. It also allows components to receive notifications coming from anywhere else in the system.
It may seem redundant or overkill to propose 5 different communication channels for a single component, the following aspects were taken into consideration for proposing all these channels:
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Components hosted at the same JVM container can reference one another using the Component API. It’s mandatory to use dependency injection as prescribed by JSR-330 (Dependency Injection) and/or JSR-346 (CDI 1.1).
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RPC is the preferred choice for communicating components hosted at different containers given that this technology provides remoting capabilities for interacting through a well known API interface. RPC fosters one-to-one communication and both synchronous and asynchronous communication.
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The Event Bus is needed for a component that can requires broadcasting data to multiple components. It also enables a component to be notified of incoming data without having a direct reference to the source or sources of said data. The communication in this channel should be asynchronous.
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The Remote Presentation Model channel is used solely for UI facing components. Their logic and behavior reside solely at the server side, simplifying the construction of new UIs without altering standard component behavior.
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Finally the REST channel is used as the last alternative for components to expose data and behavior to clients that do not support the Presentation Model, or are implemented using a programming platform other than the JVM (such as mobile devices like iOS or Android).
The following picture shows the interaction of 3 different OpenMDM® components, two of which are located within the same JVM process.
Please note that the OpenMDM® 5 Data Access modules are accessed by components using the OpenMDM® Connector Service. This allows the OpenMDM® Data Acess modules to be hosted at a different place, enabling replication and fail over. The communication protocol is still to be decided, most likely candidates are RPC and Messaging Queue.
Components require two additional elements in order to be managed by the OpenMDM® platform: metadata and configuration. The metadata describes the communication channels required by the component to work; it also describes the required configuration options (types and constraints). The configuration on the other hand, is the runtime instantiation of the metadata, that is, it describes the actual values required by the component in order to work.
Component metadata and configuration are managed by the OpenMDM® platform core services (Metadata Service and Configuration Service).
5.2. The OpenMDM® 5 Platform
The OpenMDM® 5 Platform defines a set of core services that are used to instantiate and manage OpenMDM® 5 Components. These core services provide additional capabilities to Components, such as the required communication channel end points for example. These are also the services which allow the OpenMDM® user to configure OpenMDM® systems and applications.
The following is a brief summary of each platform service and their responsibilities
5.2.1. Metadata Service
Responsible for locating, retrieving and storing of Component metadata. Metadata can be retrieved by their Component ID (defined in the Component’s specification).
5.2.2. Configuration Service
Responsible for instantiating and managing the runtime Configuration of a MDM Component. Given the right access permissions (granted by the Authentication service) a MDM Component may query the configuration of a dependent Component. Changes to the configuration of a Component must trigger an event (through the Notification service) in order to inform interested parties (the updated Component and other Components) about the changes made.
A possible interface of the configuration service must look like this:
public interface IConfigurationService {
@Nonnull
IConfiguration findByComponentId(@Nonnull String componentId);
@Nonnull
IConfiguration load(@Nonnull String componentId);
void persist(@Nonnull String componentId, @Nonnull IConfiguration configuration);
}5.2.3. Bootstrap Service
Instantiates a Component by leveraging the metadata and configuration delivered by the Metadata and Configuration services. Metadata and configuration are used to locate the proper communication channels (using the Communication service) that the MDM Component requires. It also registers the required notification listeners (via the Communication service). Finally it registers monitoring hooks (via the Monitoring service).
A minimal bootstrap service looks something like this:
public interface IBootstrapService {
@Nonnull
Set<String> getAvailableComponentIds();
@Nonnull
Set<String> getInitializedComponentIds();
boolean isComponentAvailable(@Nonnull String componentId);
boolean isComponentInitialized(@Nonnull String componentId);
@Nonnull
IMDMComponent instantiate(@Nonnull String componentId);
void shutdown(@Nonnull String componentId);
@Nullable
IMDMComponent findInstantiatedById(@Nonnull String componentId);
}5.2.4. Authentication Service
Provides integration with specific authentication mechanisms (such as LDAP) that exist in the target organization. Components and services rely on proper authentication and authorization in order to perform their duties.
5.2.5. Communications Service
Defines and manages all supported communication channels (RPC, REST, Event Bus, Presentation Model).
5.2.6. MDM Connector Service
The MDM Connector Service is a core service of the MDM Platform®, literally the glue which brings the MDM components and the MDM Data Access module(s) together. Its main purpose is to support multiple data stores or more generally to ensure the communication between distributed elements (MDM components and the MDM Data Access module can each be on different physical places).
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It knows which data stores are available including their meta data.
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It broadcasts the information about which data stores are available to the event Bus
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It aggregates data returned from different data stores.
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It allows to run MDM components and the MDM Data Access modules on different locations by communicating via RPC.
The MDM Connector Service consists of three parts:
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the MDM Connector Service: The core where the data store registry and the notification is implemented
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the MDM Data Consumer: The (client) part which connect MDM Components with MDM Connector Service Core
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the MDM Data Provider: The (server) part which connects the MDM Data Access module with MDM Connector Service Core
All parts work know and use the MDM entities (business object models). Apart from the fact that the MDM Data Consumer is aware of the location(s) the query API of the MDM Data Consumer is identical to the query API of the MDM persistence layer. See also [supporting multiple datastores]
Supporting Multiple Datastores
Multiple data sources can exist at any given time (ODS datastores, ATFX files, etc) and be made accessible to the OpenMDM® systems running on a customer’s site. There can be additional data sources outside of a particular physical site, e.g Germany and China offices. The OpenMDM®applications should be able to handle multiple data sources independently of their location. These data sources can be seen as one single element from the point of view of consumers of the MDM Connector Service. Thus this service provides a single entry point within the system, abstracting away any concerns regarding distributed transactions and data source locations. The OpenMDM® query API must be able to receive an additional argument/property that specifies the desired location or locations to be queried. If no location is given then a default (configurable) location will be assumed. The configurable default location can point to a unique datastore, a subset of all available datastores or all available datastores; it’s up to every member of the OpenMDM® Customer to decide how they want this customization to be made. The following figure depicts the interaction of an OpenMDM® Component with multiple data sources, through the MDM Connector Service:
For the purpose of Big Data consumers, an specialized component can be built on top of the MDM Connector Service so that it makes better use of the different locations, and perhaps provide some level of data caching.
5.2.7. Monitoring Service
Enables access to runtime statistics for each Component. Can be implemented using JMX technology or similar.
5.2.8. Additional Services
Other core services that may be considered are:
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Logging - general facility for asynchronous logging of messages and exceptions.
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Auditing - trace all operations performed by users and/or automated processes.
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Internationalization - resolve messages bound to a Locale.
5.3. The OpenMDM® Data Access Module
The OpenMDM® 5 Data Access module is comprised of 3 parts:
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The MDM API or core. This is the layer that defines MDM entities (business object model or bom), their relationships and interactions.
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Persistence. This layer is responsible for storing and retrieving data to and from a specific persistence solution. The ODS Adapter is an specialized solution that can handle ASAM ODS. Other persistence solutions can be hooked on too, for example simple text files, very useful for automated testing when an ODS server is not available.
External tools can consume and publish data to ODS directly. They also have the possibility to issue OpenMDM® based queries and expect an ODS specific response. This behavior will be provided exclusively by the ODS Adapter for the following reasons:
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Shield the MDM API form any ODS and/or CORBA features.
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External tools relying on this behavior require tighter integration with ODS.
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Additional persistence adapters need not implement ODS related behavior.
It’s worth mentioning that any external tools can communicate directly to the underlying data sources (in this case ODS) without affecting the MDM API nor its components.
The MDM API should provide the ability to query any MDM entity using a simple and transparent API, that is, no additional nor hidden remote calls should be executed. The past release of the OpenMDM® API (version 4) turned out to be inefficient in terms of performance due to values being queried over the wire constantly using CORBA. MDM entities must be designed as simple POJOs, property values either exist or not. If a value does not exist then an explicit query must be made to retrieve it, in other words, no special proxies (like the ones used by Hibernate) must be in place.
The query API consists of the following 5 parts with the following capabilities
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MDM Criteria API: build a query object using a programmatic API, similar to (but not necessarily identical) to the JPA Criteria API.
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MDM predefined Queries: simple API for finding entities via attributes, e.g. findByID.
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MDM functions: build specialized queries that can access native persistence finders, such as ODS functions.
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MDM String Queries: build a query using a literal representation, similar to (but not necessarily identical) to JPQL. These queries get translated into MDM Criteria queries and are thus pure convenience for developers.
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MDM Stream API: build queries to access a big amount of data / allow accessing a lot of data in a very efficient way. (TODO Andres)
The query API can also be influenced by jOOQ's design.
5.3.1. MDM Criteria API
to be described by EPOS
5.3.2. MDM Predefined Queries
to be described by EPOS
5.3.3. MDM Functions
to be described by EPOS
5.3.4. MDM String Queries
to be described by EPOS
5.3.5. MDM Stream API
to be described by EPOS
6. OpenMDM® Architecture Layout
All the pieces described in previous sections can be out together in one big picture. Once again the following applies:
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Applications are composed by putting components together via configuration (OpenMDM® Platform)
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UI based applications communicate with components using 2 channels:
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the Remote Presentation Model for those applications that be online 100%.
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the REST channel for those that require offline capabilities or do not have a Remote Presentation Model implementation.
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Components are hosted within OpenMDM® platform containers.
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OpenMDM® platform containers deliver the necessary services and facilities for components to be instantiated and communicated with one another.
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Each container runs on its own JVM process, separate form the others. Remote components.
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The MDM Connector Service of the OpenMDM® platform shields components from dealing with distributed transactions and provides multiple data source support.
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Each instance of a particular OpenMDM® API tied to a single data source runs on its own JVM process.
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The OpenMDM® data access module contains a persistence layer that allows the API to be independent of the actual storage solution (ODS, ATFX, etc).
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The yellow component should be connected to its server side counterpart, however it was left out from the diagram to keep it simple.
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Most of the services of the OpenMDM® platform have been omitted for simplicity.
6.1. Standalone Rich Applications
So far the design around OpenMDM® Components has been centered in one fact: components are hosted at a server side location. This means client applications must have an active connection to the server in order to reap the benefits of this design. However it should be possible to package all required components in the same deployment unit (the application), functioning as a monolithic rich application. In order to accommodate this requirement all packaged components require an embedded container that supplies the core facilities needed by OpenMDM® components to work at their full capacity. Additional configuration will be needed in order to instruct components to connect to local data sources (ATFX files for example) instead of reaching out to a remote ODS data source. Applications working under this model can thus sever their connection to the server when not required; the possibility to synchronise back data has to be designed and specified.
The following picture shows how such an application could look like in terms of its components
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The MDM Platform contains all required core services.
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All core services can be delivered in two implementations: offline and online enabled.
7. Runtime Configurations
Given the previous explanations on how applications can be assembled as composites of OpenMDM® the following scenarios become available for deployment given different zones. We consider the following type of applications:
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web applications
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rich client applications
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standalone rich client applications
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mobile applications
7.1. Local Zones
Both application and server components reside within the same local zones, e.g, Germany. Local zones may have network controls in place, for example firewalls. All type of applications can connect to the servers without the need of third party networking software.
7.2. Remote Zones
Remote zones can host either client or server software parts. Typically it may be just the client part (or at least that’s where the bulk is expected). Applications may be accessed in two ways:
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client side connects to the server side using the same mechanism as in the local zones. There will be added network controls between zones (stronger encryption, more than 1 firewall, etc).
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users require a remote desktop connection to a computer at the other zone where the real application can be run. In this case the real application is configured exactly as a locally running application (the prior section). The remote desktop connection software does not belong to the OpenMDM® architecture; the technologies and products used to fulfil this behavior are up to the customer’s discretion. This option is preferred where installation of software is restricted at the working site. Can only be used for rich client and web applications.
8. OpenMDM® Component Specification and Validation
The Specification of an OpenMDM® Component defines the minimum behavior required for a particular component within the OpenMDM® space. The Architecture Committee is responsible for reviewing and approving specifications. The specification of a component must:
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Define the base behavior, this is known as the MDM Component API.
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Define which communication channels are needed: RPC, REST, Event Bus, Presentation Model.
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Each channel is described using Java interfaces, enums and annotations only. Concrete and abstract classes may be included on case by case basis, validated by the OpenMDM® Architecture Committee. Constraints must be specified using JSR-303 (Bean Validation). Optionally JSR-305 (Annotations for Software Defect Detection) annotations may be used to specify nullability, immutability and thread-safety constraints.
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For the Presentation Model channel, it must include the following:
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Attributes
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name
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type
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description
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constraints (such as number range size, validation masks, etc)
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Models
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id
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description
-
attributes collection
-
-
Actions
-
id
-
description
-
-
-
For the REST channel, it must include the following:
-
A set of URLs that can be used with the HTTP verbs: GET, POST, PUT and DELETE.
-
Each URL must define its inputs
-
Each URL must define the format of its outputs. Good examples of well behaving and documented REST APIs are
-
For the REST channel, input and outputs defined in JSON format must provide a JSON schema. Inputs and outputs defined in XML format must provide an XML schema. The target format for this documentation is HTML.
-
-
For the RPC channel, it must include the following:
-
Events
-
name
-
description
-
data payload
-
-
Architectural checks to ensure compatibility of an MDM Component:
-
All data acces of an MDM Component must go through the MDM Connector Service as described in
-
Each MDM Component has a defined life cycle and must implement the IMDMComponent interface with the methods: These life cycles methods must be accessible through all supported channels:
public interface IMDMComponent {
void init(@Nonnull IConfiguration configuration);
void update(@Nonnull IConfiguration configuration);
void destroy();
}-
If the MDM Component needs to be configurable (most likely), it must provide documentation and information on how the component needs to be configured. The configuration consists of key value pairs and must be accessible via the following interface:
public interface IConfiguration {
@Nullable
Object get(@Nonnull String key);
@Nullable
Integer getAsInteger(@Nonnull String key);
@Nullable
Boolean getAsBoolean(@Nonnull String key);
@Nullable
Double getAsDouble(@Nonnull String key);
@Nullable
String getAsString(@Nonnull String key);
}-
i118n: Each MDM Component must use the internationalization Module/API (yet to be defined) for the internationalization of Asm ODS domain content. If the MDM component contains other date which needs to be internationalized, it must make use of the internationalization service mentioned above. For MDM Components with an UI, the internationalization information must be provided by the presentation model.
The checklists mentioned above are the Test Compatibility Kit (TCK) for an OpenMDM® 5 component. It must be evaluated manually by the committers and the Architecture Comittee.
The Component Test Compatibility Kit (CTCK) is a set of functional tests that every component implementation must pass. The CTCK must be developed at the same time as the component’s specification and finished no later than the first concrete implementation of said component specification. The OpenMDM® Architecture Committee is the ultimate responsible for reviewing and accepting a CTCK.
9. Summary
The Architecture Design for OpenMDM® 5 components is defined in terms of logical boundaries and desired behavior, following the driving forces and architecture goals. The OpenMDM® Architecture Committee is responsible for the review and vote of technologies and products that can fulfil the goals described in this document.
10. Glossary
Component Technology Compatibility Kit. This is a programmatic test harness that ensures a mdm component is compliant to an particular component specification.
Java Specification Request. The formal documents that describe proposed specifications and technologies for adding to the Java platform. A final JSR provides a reference implementation that is a free implementation of the technology in source code form and a Technology Compatibility Kit to verify the API specification. Wikipedia
Java Platform, Enterprise Edition or Java EE is Oracle’s enterprise Java computing platform. The platform provides an API and runtime environment for developing and running enterprise software, including network and web services, and other large-scale, multi-tiered, scalable, reliable, and secure network applications. Java EE extends the Java Platform, Standard Edition (Java SE),[1] providing an API for object-relational mapping, distributed and multi-tier architectures, and web services. The platform incorporates a design based largely on modular components running on an application server. Software for Java EE is primarily developed in the Java programming language. Wikipedia
Java Virtual Machine. A Java virtual machine is an abstract computing machine. The Java virtual machine is called "virtual" because it is an abstract computer defined by a specification. JVM specification omits implementation details that are not part of the Java virtual machine’s specification. For example, the memory layout of run-time data areas, the garbage-collection algorithm used, and any internal optimization of the Java virtual machine instructions (their translation into machine code). The main reason for this omission is to not unnecessarily constrain the creativity of implementors. Any Java application can be run only inside a run-time instance of some concrete implementation of the abstract specification of the Java virtual machine. Wikipedia
An application using one or more MDM components. Applications typically have on part on the client and one one on the server. They require an MDM system running.
Since component is a term often used and in different context, if we speak of OpenMDM® or MDM components, we mean components which have a specific architecture as described in [Anatomy of an OpenMDM® Component] above. While [the OpenMDM® Data Access] of course is an architectural component or module as are the MDM Connector Service and other services they are not OpenMDM® components and we should avoid calling them that.
An MDM System is the assemply of all the modules needed to run one or more MDM applications on top of it. It typically consists of one or several MDM Data Access modules, of the MDM Platform, one or several MDM components and one or several MDM applications.
A remote procedure call (RPC) is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space (commonly on another computer on a shared network) without the programmer explicitly coding the details for this remote interaction. That is, the programmer writes essentially the same code whether the subroutine is local to the executing program, or remote. Wikipedia
Technology Compatibility Kit. This is a set of rules and guidelines that must be validated in order to assert that a particular component specification is compliant to the OpenMDM® Component Specification. Java TCK @ Wikipedia
11. References
[1] Bradner, S., Key words for use in RFCs to Indicate Requirement Levels
http://tools.ietf.org/html/rfc2119