1 karl  1.1 /*
  2           */
  3           

  4 karl  1.4 /** @name Pegasus Architecture

  5 karl  1.1 

  6 karl  1.2 This section defines the overall architecture of the Pegasus implementation.

  7 karl  1.1 

  8 karl  1.4 */
  9           //@{
 10           /** @name Design Goals

 11 karl  1.1 

 12 karl  1.4 The Pegasus design team set some basic design goals early in the development of Pegasus as follows:

 13 karl  1.3 <UL>
 14           <LI>C++ as the core development language. We selected C++ because it represented a compromise between the ability to work with objects and a language that would be acceptable for high avaailablity platforms.
 15           <LI>Modular Architecture - We wanted to be able to create the architecture based on well understand standardized modules that have clean well defined interfaces between the modules.
 16           <LI>Open to a wide range of specialization and customization.
 17           <LI>Minimize the functionality of the basic core CIMOM. We wanted to create an environment where the majority of customization could be created by working with attached modules that would both extend and modify the functionality of the broker.
 18           <LI>Use only open source components in the pegasus environment
 19           <LI>Design for maximum portability. The initial targets would be Linux, Unix, and NT but the product should be usable in a wide variety of platforms and platform sizes.
 20           <LI>The APIs and interfaces should be clear, given that they are in C++
 21           <LI>
 22           </UL>

 23 karl  1.1 */
 24           

 25 karl  1.4   
 26           /** @name The Broker

 27 karl  1.2 
 28           The Common Information Model Object Broker (often known as the CIM Information
 29           manager or CIMOM) brokers CIM objects between a number of sources and
 30           destinations. A CIM object should be a representation, or model, of
 31           a managed resource, such as a printer, disk drive, or central processing unit
 32           (CPU). In the Pegasus implementation, CIM objects are represented
 33           internally as C++ classes. The CIMOM transfers information
 34           between WBEM clients, the CIM Object Manager Repository, and managed
 35           resources.

 36 karl  1.1 
 37           */
 38           

 39 karl  1.2 /** @name Pegasus Providers.

 40 karl  1.1 ATTN: Define in more detail
 41           
 42           */
 43           
 44           /** @name Extension Services
 45           ATTN: Document this as an architectural component
 46           */
 47           
 48           
 49           /** @name Pegasus Clients.
 50           ATTN: define in more detail

 51 karl  1.2 
 52           */
 53           

 54 karl  1.4 /** @name Functional Flow

 55 karl  1.2 
 56           The Common Information Model Object Broker (often known as the CIM Information
 57           manager or CIMOM) brokers CIM objects between a number of sources and
 58           destinations. A CIM object should be a representation, or model, of
 59           a managed resource, such as a printer, disk drive, or central processing unit
 60           (CPU). In the Pegasus implementation, CIM objects are represented
 61           internally as C++ classes. The CIMOM transfers information
 62           between WBEM clients, the CIM Object Manager Repository, and managed
 63           resources.
 64           
 65           NOTE: We are very careful in the use of CIM and WBEM.  These are terms defined
 66           and controled by the DMTF and they have specific meanings both technically and
 67           legally. Thus, the objects are CIM objects.  However, the client is a WBEM
 68           client because it uses the DMTF XML/HTTP specificaitons to transfer
 69           information and that specification and CIM form WBEM.
 70           
 71           When a WBEM client application accesses information about a managed
 72           resource, the CIM Object Manager contacts either the appropriate provider
 73           for the CIM object that represents that managed resource or the CIM Object
 74           Manager Repository. Providers are classes that communicate with managed
 75           objects to retrieve data. If the requested data is not available from the CIM
 76 karl  1.2 Object manager Repository, the CIM Object Manager forwards the request to
 77           the provider for that managed resource.
 78           
 79           Using the Repository.
 80           
 81           The provider dynamically retrieves the requested information, which is sent back to the requester. The CIM Object Manager Repository only contains static data. Classes that are handled by a provider must have a Provider qualifier that identifies the provider to contact for the class. When the CIM Object Manager receives a request for a class that has a Provider qualifier, it should route the request to the specified provider. If no provider is specified, it should route the request to the CIM Object Manager Repository.
 82           
 83           When a WBEM client connects to a CIM Object Manager, it will get a handle to the CIM Object Manager. The client can then perform WBEM operations.using this reference. At startup, the CIM Object Manager should perform the following functions: Listen for RMI connections on RMI port 5987 and for XML/HTTP connections on HTTP.
 84           
 85           NOTE: The current version of the CIMOM does not incorporate events.  Therefore, this description is written around a CIMOM without events functionality.
 86           
 87           Note - The listener for connections may not be the Object Manager; it could
 88           be another entity that is performing the operation for the Object Manager.
 89           This could be a servlet in a Web server. Conformant object managers are
 90           required to support XML over HTTP - Pegasus is conformant.
 91           
 92           The CIMOM accepts requests called WBEM Operations from the WBEM client. These operations are explicitly defined in the WBEM specification. They represent the operations possible on CIM objects (ex. create/modify/delete class/instance, etc.) During normal operations, the CIMOM performs the following for each operation request received:
 93           <UL>
 94           <LI>Security checks to authenticate user login and authorization to
 95           access the CIMOM information.
 96           <LI>Syntactic and semantic checks of the CIM data operations to
 97 karl  1.2 ensure that they comply with the current version of the CIM
 98           specification.
 99           <LI>Route requests to the appropriate provider orthe Repository.
100           The CIMOM iteself does not serve as a Repository for CIM class definitions and instance data. Persistence is provided by the Repository; however, the contact point is the CIMOM. Thus, the Repository could be considered as an option except that the CIMIM is required to keep class information for all semantic and syntatic confirmation and therefore the class repository is a requirement of a working CIMOM, not an option.
101           <LI>Deliver data from providers and from the CIM Object Manager
102           Repository to the originating WBEM client application.
103           </UL>
104           The CIMOM should be a process that accepts requests for CIM
105           operations, as defined by the DMTF, and carries out these operations.  The
106           Pegasus CIMOM runs as a daemon process that waits for requests.
107           
108           <B>Authentication</B>
109           
110           Before any requests can be made to the CIM Object Manager, an
111           authenticated session must be established.  
112           
113           NOTE:The current version of Pegasus does not
114           have any authentication.  However, it is planned for version 1.1.
115           
116           An identifier for the user and optionally a role will be associated with the authenticated session. A role is a principal identity associated with the current session, in addition to the user identity. Systems that do not support roles can ignore them as described in the Security Interface. These can be maintained in an internal Hash map.
117           
118 karl  1.2 <B>Request Reception</B>
119           
120           The CIMOM receives requests through CIM operations over HTTP. Each request will be associated with a session that is set up as part of the initial authentication exchange. Since the session has an associated user, each request automatically has a user associated with it. This should be useful for authorization checking for a given request. Once the request has been received, the appropriate components for handling the specific request will be invoked. The Pegasus implementation has methods for each of the major CIM operations over HTTP. Once the request is received, the appropriate method will be called..
121           
122           <B>Authorization</B>
123           
124           The default implementation is Access Control List (ACL) based. Access
125           control lists can be maintained per namespace or on a per namespace/user
126           basis. These lists will be maintained in the root/security namespace. The CIM
127           Object Manager will grant read or write permissions within a namespace
128           based on the access control list. Since CIM operations are done within the
129           context of a namespace, these ACLs will enforce rules on whether an
130           operation should be allowed. For operations that will ultimately be handled by
131           a provider, the appropriate provider can replace the authorization scheme.
132           This will allow providers to enforce finer grained control if desired. A
133           provider
134           can replace the default authorization checking scheme by implementing the
135           Authorizable interface. If implemented, no calls are made to the CIM Object
136           Manager.
137           
138           <B>Provider</B>
139 karl  1.2 
140           <B>Provider RegistrationB/B>
141           
142           The Pegasus CIMOM enables developers to write providers, which serve dynamic information to the CIMOM (see Providers).  Providers register themselves by specifying their location in a Provider qualifier. Providers can be set up on a class, property, or method basis. Providers can have one or more of the different provider types. The DMTF CIM specification allows the Provider qualifier to have an implementation specific interpretation. For Pegasus, the Provider qualifier constitutes the executable name of a provider executable implementing the provider functions for the class. 
143           
144           
145           There are a number of conceptual interfaces that can be implemented by providers:
146           <UL>
147           <LI>InstanceProvider
148           <LI>MethodProvider
149           <LI>PropertyProvider
150           <LI>AssociatorProvider
151           </UL>
152           .
153           Each conceptual interface provides a subset of the WBEM Operations as follows:
154           
155           NOTE: ATTN: Table defining the types vs. operations
156           
157           However
158           
159           Providers should be loaded "on
160 karl  1.2 demand" by the CIMOM. Classes and properties marked by the
161           provider qualifier will be an indication to the object manager that the
162           associated information is dynamic and must be obtained from the providers
163           rather than the repository. When the object manager determines that a
164           specific request needs dynamic data, provider should be
165           loaded and instantiated. Additionally, the "initialize" method of the Provider
166           will be invoked. There should be only a single instance of the provider.
167           
168           ATTN: Review the following:  In the reference implementation, the ProviderChecker maintains a hash map of all the providers. This will enable the CIM Object Manager to load a provider only if it has not been loaded previously. There should be no specified time when a provider can be "unloaded", however providers have a "cleanup" method that can be invoked if, and when, this behavior is specified for the object manager.
169           
170           The CIM Object Manager will not act as as a provider for
171           classes. However, there are instances where classes must interact with the CIMOM itself. These might include authentication classes, authorization classes, namespace classes, and classes that provide information on the CIMOM iteslf.
172           
173           These classes will be handled by providers but these will be specialized providers that have access back to the CIMOM itself.  All of this is being defined as part of a services extension interface to PEGASUS.  This interface will be discussed in a future version of this document:
174           
175           ATTN: add the services interfaces.
176           
177           
178           
179           
180           ATTN: Dealing with multiple providers per class.
181 karl  1.2 
182           
183           <B>Request Routing</B>
184           
185           One of the main functions of the CIMOM is operation request routing.
186           Depending on the request, the request may need to be authorized and passed to
187           semantic checkers, providers, and the repository.
188           
189           Requests may be for static information such as schema
190           definitions or static instances. In this case, the CIMOM should
191           route the request to the proper repository.
192           
193           The more complex routing will involve operations that can traverse multiple
194           classes and their instances. An example of such an operation is association
195           traversal. In order to determine the associated instances of a given input
196           instance, the CIMOM should first determine the associations
197           that the given instance class participates in. It will obtain this from the
198           associations that have been compiled and stored in the repository. Once
199           these associations are determined, the CIM Object Manager should find
200           those instances of the associations in which the given input instance plays a
201           role. These associations may, or may not be, dynamic. Depending on
202 karl  1.2 whether the associations are dynamic or not, the CIM Object Manager may
203           route the requests to providers or the repository. Once the results are
204           returned, they should be concatenated together and returned because of the
205           request. The CIM Object Manager will use schema information to determine
206           which providers to contact. As can be seen, a given request can result in
207           multiple sub-requests to the providers or the repository.
208           A similar situation will occur when a deep enumeration is performed on
209           instances of a class.
210           
211           <B>Semantic Checking</B>
212           
213           The CIMOM performs semantic checks before classes or
214           instances can be set or createdusing internal class,
215           property, instance, method, and qualifier checkers and the rules ov validation defined by the CIM specification. These verifiers ensure that the CIM rules are enforced. This includes type verification,type conversions, verification of proper key usage, and other checks.,

216 karl  1.1 
217           */

218 karl  1.4 //@}

219 karl  1.1