The purpose of this document is to define the structure of OpenMDM® 5 components and their relationship with the OpenMDM® 5 Business 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® Business Model.
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 component 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 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® Business Model. The OpenMDM® Business Model 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® Business Model, 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. The Component Specification for this channel should be written using Java interfaces, enums and annotations only. Concrete and abstract classes are to be included on rare occasion, validated by the OpenMDM® Architecture Committee. Constraints must be specified using JSR-303 (Bean Validation) and JSR-305 (Annotations for Software Defect Detection) annotations.
Used exclusively by UI clients that support the Remote Presentation Model pattern. This channel must be used to build up Rich and Web clients. The Component Specification 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
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attributes collection
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Actions
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id
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description
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The language used to describe these elements must be Java, making use of interfaces, annotations and enums only. Constraints must be specified using JSR-303 (Bean Validation) and JSR-305 (Annotations for Software Defect Detection) annotations.
Used by clients that require offline capabilities and/or those that do not support the Remote Presentation Model pattern. The Component Specification must include the following:
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A set of URLs that can be used with the HTTP verbs: GET, POST, PUT and DELETE.
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Each URL must define its inputs
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Each URL must define the format of its outputs
Good examples of well behaving and documented REST APIs are
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.
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. The Component Specification for this channel includes Java interfaces, enums and annotations only. Constraints must be specified using JSR-303 (Bean Validation) and JSR-305 (Annotations for Software Defect Detection) annotations. The chosen RPC technology may impose additional restrictions to the Component Specification.
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. The Component Specification should include the following:
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Events
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name
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description
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data payload
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The Component Specification must be in terms of the chosen technology for implementing an Event Bus. In the case of the technology being JMS it should conform to JSR-343 (JMS 2.0).
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 to interaction 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 Business Model can be accessed by components using an OpenMDM® Connector. This allows the OpenMDM® Business Model 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.
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.
The following is a brief summary of each 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 Component. Given the right access permissions (granted by the Authentication service) a 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.
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 Component requires. It also registers the required notification listeners (via the Notification service). Finally it registers monitoring hooks (via the Monitoring service).
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
Grants access to the MDM API.
5.2.7. Notification Service
A specialized communication channel used to send and receive events from the OpenMDM® platform. It may be implemented using the same technology chosen for the Event Bus channel.
5.2.8. Monitoring Service
Enables access to runtime statistics for each Component. Can be implemented using JMX technology or similar.
5.3. The OpenMDM® Business Model
The OpenMDM® 5 Business Model is comprised of 3 layers:
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The Component API or core. This is the layer that defines MDM entities, their relationships and interactions.
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The Connector. This layer is responsible for exposing the core layer to the outside world, that is, the OpenMDM® components.
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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 exists 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 must provide the following capabilities
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build a query object using a programmatic API, similar to (but not necessarily identical) to the JPA Criteria API.
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build a query using a literal representation, similar to (but not necessarily identical) to JPQL.
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build specialized queries that can access native persistence finders, such as ODS functions.
The query API can also be influenced by jOOQ's design.
5.3.1. 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® Business Model 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 services provides a single entry point within the system, abstraction 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 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 chaching.
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.
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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 containers.
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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 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® API has a persistence layer that allows the API to be independent of the actual storage solution (ODS, ATFX, etc).
7. OpenMDM® Component Specification
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spec defines the API.
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component defines which channels must be used (PM, REST, RPC, EB).
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Each channel is describe using Java interfaces, enums and in some cases, abstract and concrete classes. All parameters and return types must be annotated with JSR-303 (Bean Validation) and JSR-305 (Annotations for Software Defect Detection) annotations.
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UI delivers mockups and usability guidelines.
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Common project layout.
8. Summary
TBD
9. Glossary
Component Technology Compatibility Kit. This is a programmatic test harness that ensures a component is conformant 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
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 conformant to the OpenMDM® Component Specification. Java TCK @ Wikipedia
10. References
[1] Bradner, S., Key words for use in RFCs to Indicate Requirement Levels
http://tools.ietf.org/html/rfc2119