Architectural design of MDX compiler via attribute-driven design *

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1 Jul. 2009, Volume 6, No.7 (Serial No.56) Journal of Communication and Computer, ISSN , USA Architectural design of MDX compiler via attribute-driven design * ZHANG Ping-jian, XI Jian-qing, ZHAO Juan-juan (School of Software Engineering, South China University of Technology, Guangzhou , China) Abstract: MDX is a language that expresses selections, calculations, and some metadata definitions against an Online Analytical Processing (OLAP) database. As the interface with OLAP, the MDX complier is a major component of the OLAP analysis server. This paper addresses the system design of MDX compiler via the ADD method, meaning that system requirements, including functional and quality requirements and constraints, are considered as drivers in the design process. The output architecture satisfies not only that the functional requirements but also the important qualities the system must possess. Key words: MDX complier; OLAP analysis server; software architecture; attribute-driven design 1. Introduction Multi Dimensional expression (MDX) is a language for OLAP query, computation and meta data definition, proposed jointly by Microsoft and Hyperion around MDX works with data warehouse similarly to how SQL works with DBMS. With growing support from OLAP vendors, MDX has become the de facto standard for OLAP manipulations. As the interface with OLAP services, the MDX compiler is one of the major components of the OLAP analysis server, and its design and implementation is critical to the success of OLAP * Acknowledgements: The research was supported by the Science & Technology Project of Guangdong Province (No. 2006B ) and the Science & Technology Project of Guangzhou City (No. 2006Z3-D3081). Corresponding author: ZHANG Ping-jian (1966- ), male, Ph.D., associate professor; research fields: data warehouse, software engineering. XI Jian-qing (1962- ), male, Ph.D., professor; research fields: database, high performance computing, knowledge engineering. ZHAO Juan-juan (1975- ), female, lecturer; research fields: data mining, knowledge engineering. server. This paper focuses on some design issues of a MDX compiler. In traditional software architecture design, functional requirements are emphasized and are always satisfied, with little consideration of quality requirements. In reference [1], Chung, et al considers that quality attributes are soft goals; there is no clear-cut definition and criteria as to whether it is satisfied or not. In the work of Bosch, et al [2], the functional requirement is the primary driver and the quality attribute as secondary driver. Hofmeister, et al [3] describe a framework known as global analysis to identify, accommodate, and describe architecturally significant factors including quality attributes early into the design phase. However, these methods do not sufficiently support the reasoning about the quality consequences of each design decision. The Attribute-Driven Design (ADD) [4], on the other hand, considers both as primary architectural drivers and has been applied in system design [5-6]. In this paper, we discuss the design of an MDX compiler via the ADD approach. Both functional and non-functional requirements are analyzed using use cases and quality attribute scenarios. Usually, stakeholders participating in the decision-making process have different, often conflicting, quality goals (e.g., performance, security, availability, modifiability, and usability), and project constraints. By prioritizing the quality attribute scenarios, we ensure that the most important qualities are satisfied first; the secondary qualities are satisfied within the constraints of the most important ones. Tactics and primitives to achieve system qualities are proposed and applied in the design process. 1

2 2. The add design method ADD is basically built upon Attribute Based Architecture Styles (ABAS) [7], and architectural views [8-9]. It provides a framework to make design decisions with known affects on the desired quality attributes. The input to ADD is the system requirements (i.e. functional, quality requirements and constraints), and its output is the conceptual architecture which provides the overview of data and control transfer between system components. Further instantiation and decisions on conceptual architecture would yield the concrete architecture, the document that is the basis for discussion among various stakeholders. The ADD steps go as follows: (1) Choose the module to decompose. Initially, this is the system or subsystem under design. (2) Refine the module according to the following steps: (a) Choose the architectural driver from the set of concrete quality scenarios and functional requirements. This will determine what is important for this decomposition; (b) Choose an architectural pattern that satisfies the drivers. Create the pattern based on the tactic that can be used to achieve the drivers. Identify the modules required to implement the tactics; (c) Instantiate modules and allocate functionalities from the use cases and represent using multiple views; (d) Define interfaces of the child modules; (e) Verify and refine use cases and quality scenario and make them constraints for the child modules. This step verifies that nothing important was forgotten. (3) Repeat steps in (2) (a)-to-(e) for all other modules for decomposition. 3. MDX compiler requirement analysis The MDX compiler lies in between the application interface layer and OLAP business layer [10]. It receives the MDX statements and converts them to some query tree objects, which are passed down to the business layer for processing. Results are returned to clients via the application interface layer. The architecture of the OLAP server is portrayed in Fig. 1. Fig. 1 Architecture of the OLAP server 3.1 Functional requirements of MDX compiler The MDX compiler consists of 5 modules: database connection module, metadata access module, MDX parser module, calculated member and function evaluation module, and authentication/ authorization module. After obtaining the MDX statements, the MDX compiler connects to database and retrieves the data warehouse metadata information, which is used to parse those statements. When abstract syntax trees are constructed, metadata information is further employed to handle the calculated members and function evaluations. Finally, query tree objects are constructed for subsequent processing. The MDX compiler use cases are summarized below: (1) The end edits MDX statements in some text area and then submits. 2

3 (2) The end manipulates with GUI controls and generates MDX statements to submit. (3) The MDX compiler checks not only syntax validity but also semantics integrity and consistency. (4) The statistics and report subsystem requires routine OLAP querying at daily/weekly/monthly base. (5) The decision support subsystem regularly requests OLAP querying for data mining services. (6) Other applications can interact with OLAP server for OLAP services via API. (7) MDX compiler accesses database for necessary metadata information and consults the authentication and authorization subsystem to ensure valid OLAP services request. (8) MDX compiler accesses database for necessary metadata information to handle calculated members and function evaluations. 3.2 Quality attributes requirements of MDX compiler Quality attributes are the functional characteristics that the system must possess. Some of these qualities are overlapping (e.g. availability vs. security) and often the achievement of one has a side effect on another (e.g. security vs. performance). The ADD method, therefore, is aimed at satisfying the desired primary qualities and the achievement of secondary attributes is only within the constraint of achieving the primary ones. For MDX compiler design, its basic qualities to achieve are (i) availability, (ii) modifiability, (iii) performance, (iv) security, (v) portability, and (vi) inter-operability. Availability is about diagnosing, solving and preventing ML software and its associated hardware from faults and failures. Modifiability is about ease in installing changes to ML system. Performance is making sure that the system is able to respond accordingly when an event occurs. Security is about protecting the system and its s and finding ways to deny access to unauthorized s. Portability refers to that quality of the system that could be easily configured and deployed to other platform. Inter-operability is the ability to interact with other and applications. Achieving these qualities depends on the system s capacity to respond correctly on different stimuli that could challenge the system from achieving these qualities. Table 1 provides the MDX compiler quality attribute scenarios. For each quality attribute (e.g. availability), different stimuli are conceived, and it shows how the system would respond. The success of the response is based on its ability to satisfy the response measure. Quality attribute Availability Modifiability Modifiability Performance Table 1 The MDX compiler quality attribute scenarios Stimulus Source of stimulus Artifact Response Response measure Hardware failure; Log error; inform ; Downtime should be CPU failure All modules corrupted programs start backups less than 5 minutes Fact table; Log error; inform ; Recovery data within 1 Database failure Corrupted data aggregate data recover data minutes Request to add XMLA Project manager; Query tree Extend query tree Complete within 1 support architect person week Request to support new Project manager; Query tree Extend query tree Complete within 1 MDX features end Request to support new Project manager; Query tree Extend query tree Complete within 2 end OLAP services request Analyst; tester; end MDX compiler; Parse MDX statement Data retrieved within from console retrieve aggregate data half minute OLAP services request Analyst; tester; end MDX compiler; Parse MDX statement Data retrieved within from Report /Data retrieve aggregate data 30 minute mining OLAP services request from other Other MDX compiler; Parse MDX statement retrieve aggregate data Data retrieved within 1 minute (to be continued) 3

4 Security Portability Interoperability Invalid Invalid access Request to port system to other platform Request to operate with other s and front end BI Other or Any data in Validate persons Other or Sensitive data in Authorize persons Module that is Customer Project platform lead dependent Other OLAP engines and BI MDX compiler; Modify the dependent modules Interact with other or other Deny system to invalid Deny data to invalid access Complete within 3 Able to retrieve data from other OLAP engine; able to interact with other BI 4. Attribute-driven design of MDX compiler The design begins with identification of the most important quality attribute issues of MDX compiler. In Table 1, the two availability scenarios are in fact shared by all sub of the OLAP server, and hence is not the focus of this paper. After reviewing those scenarios, the project team becomes congruous that for a robust MDX compiler, it is imperative to consider the modifiability above all others. The OLAP service and the MDX language are prospecting new technologies that are still under rapid development, new concepts, specifications, architectures, frameworks and APIs are emerging. To meet the challenge, MDX compiler needs to be design for flexibility and extensibility. Closely related to modifiability is the inter-operability, which is becoming the core idea of enterprise service infrastructure. The second top priority attribute is the performance, which is always among the most important indexes of any good. For MDX compiler, performance is not a big deal since query tree objects are usually quite small, especially for those from interactive s. Of course, some reporting/data mining services might generate quite complicated MDX statements. The only problem here is that there should be some preemptive policy to guarantee that interactive s will not wait too long. Security has become a more and more important issue for any information system, the data warehouse and OLAP server is not an exception. Incorporation of authentication and authorization into MDX compiler makes it possible for early detection of invalid intrusion to the system and thus saves both time and resources. Currently, unlike the other quality attributes, portability is given little consideration for the first release of the MDX compiler except that only standard C++ features and standard C++ library are strictly adhered to. 4.1 Adapting architectural primitives and tactics to achieve qualities Architectural primitives are components and connectors that collaborate to achieve some quality attribute goal. The MDX compiler is designed with all the quality attribute scenarios bear on mind. To achieve modifiability, the strategy to be adapted is called indirection. To accommodate modifications, an abstract syntax tree structure is adopted. With various modification requests, concrete query tree structures are generated from the abstract syntax tree. In addition, the semantic coherence strategy and the generalize module strategy are applied to API design which allows programming to interface, not to class. To achieve inter-operability, the adherence to defined protocol strategy is adapted and the MDX compiler communicates with other sub via the standard XML/A protocol. To achieve performance, three strategies are adapted. First, resource arbitration via preemptive priority scheduling is implemented to guarantee that reporting/data mining jobs will give way to interactive s which have the highest priority. Secondly, concurrency is introduced to process requests so that the compilers will not get stuck by a time consuming 4

5 job. Finally, a small cache for MDX statements and query tree objects is maintained, and efficiency is gained at the cost of some memory space. To achieve security, in addition to the routine authentication and the role based authorization, the limit exposure strategy is also adapted, i.e., except necessary services for the OLAP server to work, other system services are all shut down. 4.2 The conceptual architectural view Architectural views represent the elements of the system and the relationship among them; it shows the modules, the possible contention and the resources allocated to a component. The architectural view of MDX compiler is depicted in Fig. 2 below. Fig. 2 Architecture of the MDX compiler 4.3 Test of the MDX compiler The MDX compiler has been implemented along with the. To ensure maximum portability, only standard C++ features and libraries are used. To test the flexibility, we have run the MDX compiler against various such as Microsoft SQL Server Analysis Services, Modrian and our proprietary OLAP server, as well as various BI such as JPivot, CubeDesigner and Pentaho. Testing results demonstrate that our MDX compiler works seamlessly with these. attributes are presented. We concur with ADD on the need to consider quality attributes, along with functional requirements and system constraints, as the drivers in the design process. References: [1] Chung L., et al. Using non-functional requirements to systematically support change. 2nd IEEE Intl. Symposium on Requirements Engineering, [2] Bosch J. and Molin P. Software architecture design: Evaluation and transformation. ECBS 99, IEEE Conf. and Workshop on Engg of Comp.-Based Systems, [3] Hofmeister, C., Nord, R. L. and Soni, D. Applied Software Architecture. Reading, MA. Addison-Wesley Longman, 2000 [4] Bachmann F. and Bass L. Intro. to attribute driven design method. Proceedings. IEEE Comp. Society Intl. Conf. on Software Engg., Toronto, Canada, [5] T. Al-Naeem1, I. Gorton, M. A. Babar, F. Rabhi and B. Benatallah. A quality-driven decision-support method for identifying software architecture candidates. ICSE 05, May 15-21, 2005, St. Louis, Missouri, USA, [6] Hina M. D., Tadj C. and Ramdane-Cherif A. Attribute-driven design of incremental learning component of a ubiquitous multimodal multimedia computing system. IEEE CCECE/CCGEI, Ottawa, May 2006, [7] M. Klein and R. Kazman. Attribute-Based Architectural Styles, Tech. Report, CMU/SEI-99-TR-022, Soft Engineering Institute, Carnegie Mellon University. [8] Kruchten P. B. The 4+1 View Model of architecture. IEEE Software, 1995, 12(6): [9] Soni D., Nord R. L. and Hofmeister C. Software architecture in industrial applications. Proc. of the 17th International Conference on Software Engineering, Washington, USA, [10] George S. and Sivakumar H. MDX solutions: With Microsoft SQL Server Analysis Services 2005 and Hyperion Essb, (Edited by Jane, Flyer) 5. Conclusions This paper covers the requirement analysis of the MDX compiler of the OLAP server. Functional and quality requirements are enumerated, with discussion on deciding the driving quality attributes. Techniques to achieve those most important system quality 5