- SQuaRE Series provides practical quality models for system and software products. However, it does not fit completely with aspects of new technologies. There are unique characteristics of cloud services, so we need special considerations when measuring and evaluating them. Therefore, a new project for standardization has started to develop a quality model and measures that guide the quality evaluation of cloud services. In this paper, we would like to share the approach we used to define the quality model for cloud services.
INTRODUCTION
ISO/IEC JTC1/SC7 is the international standardization organization responsible for standardizing software and systems engineering, which consists of 13 working groups and 5 ad-hoc groups. WG6, Working Group 6, is in charge of software product measurement and evaluation. The standards developed by WG6 are named as SQuaRE (Software product Quality Requirements and Evaluation).
SQuaRE Series provides practical quality models for system and software products. However, it does not fit completely with aspects of new technologies. There are unique characteristics of cloud services, so we need special considerations when measuring and evaluating them. Even though SC38, responsible for the standardization of cloud computing, has developed many standards for cloud computing, there is no standard for quality evaluation. It is the reason why SC7/WG6 started a new project to develop a quality model and measures that guide the quality evaluation of cloud services.
Because it is the first time to apply the existing quality models to new technology, it is important to decide how to define the new model based on the existing models. It was also important to consider alignment with standards for cloud services. With these considerations, we proposed a methodology to defining a quality model for cloud services. In this paper, we would like to share the approach we has proposed to define the quality model for cloud services.
II.
WHAT IS QUALITY AND QUALITY MODELS?
ISO/IEC 25000 of SQuaRE Series provides quality models as a defined set of quality characteristics. It provides a good framework when specifying requirements and evaluating software quality. Quality characteristic is a category of attributes relevant to software quality.
Systems and software products have eight quality
characteristics that are functional suitability, performance
efficiency, compatibility, usability and so on[
A set of quality measures is defined in ISO/IEC 2502n
which can be used to evaluate quality characteristics[
Measurement is an activity of determining a quality value against a software product based on quality model. After measurement, we can get objective values. ISO/IEC TS 25011
IT Service Quality Model
Name of Standards Guide to SQuaRE Planning and Management System and Software Quality Models Data Quality Model Measurement Reference Model Measurement of Quality in Use Measurement of Sys. & SWP Quality Measurement of Data Quality Measurement of IT Service Quality (TS) Quality Requirement Quality Evaluation Process Evaluation Guide for Developers, Acquirers and Independent Evaluators Evaluation Module for Recoverability Division Product Quality General Quality Model
Quality Measurement
Quality Requirement Evaluation III.
DEVELOPMENT APPROACH
In SQuaRE Series, there are well-defined quality models for measuring and evaluating system & software products, IT service, data, and so on. To define the quality model of cloud services, we can first use the existing models and then add new quality characteristics based on SC38 standards.
Step 1) Select quality characteristics from the existing quality models of SQuaRE Series Step 2) Suggest new quality sub-characteristics based on SC38 standards Step 3) Classify the appropriate characteristics sub-characteristics into
After the quality model is defined, the next steps to develop quality measures and a guideline are as follows: Step 4) Select appropriate quality measures from the existing measurement standards
Table Ⅱ shows International Standards and Technical Specification developed by SC7/WG6. SC7/WG6 name these standards as SQuaRE (Software product Quality Requirements and Evaluation). There are five divisions that are 1) Product Quality General, 2) Quality Model, 3) Quality Measurement, 4) Quality Requirements and 5) Evaluation.
Until now, four quality models have been developed.
ISO/IEC 25010[
Step 5) Add new measures for the newly defined characteristics Step 6) Provide the guideline for the model and measurement standards
In this chapter, we describe in detail the three steps to define the quality model.
Since CSP(Cloud Service Provider) provides a software,
platform and infrastructure as a service, cloud services
provided by CSP can be evaluated by system and software
product quality model, called ‘product quality model’, defined
in ISO/IEC 25010 [
As explained earlier, the product quality model is applicable to both computer systems and software products. The computer system includes computer hardware, software and data, not communication systems. With the cloud computing point of view, we can interpret the computer system and software products as infrastructure, platform and application provided by CSP. For this reason, we can apply this model to cloud services.
There are two types of IT services which are defined in
ISO/IEC TS 25011 [
Services completely automated provided by an IT system (type a) Services provided by a human using an IT system (type b)
According to the types of IT services, cloud services provided by CSP are highly related to ‘type a’ because they have the following characteristics: • • • •
CSC(Cloud Service Customer) provisions computing capabilities automatically or with minimal interaction with CSP One or more capabilities offered via cloud computing invoked using a defined interface. In other words, the capabilities are offered with minimal interaction
As well as type a), we also should consider type b) in some sense, because there are sub-roles of CSP, customer support and care representative that provide customer services to CSC. For this reason, we can partially apply the IT service quality model.
There are similar sub-characteristics between the product quality model and IT service quality model. For this case, we suppose that the product quality model takes precedent over the service model because CSP provides the services by using the existing functions rather than implementing new components. That is why the yellow circle is in front of the rectangle and triangle in Figure 4. Because we partially apply the IT service quality model, the partial blue rectangle is used for defining quality model of cloud services.
Because the product and data quality model can be fully applied, a full circle and triangle are used in Figure 4. Figure 5 shows SQuaRE view of the quality model development approach.
Although quality characteristics for data are implicitly connected to the product quality model, data quality model has been defined to complement the product quality model.
In case of system software such as operating systems, data quality is more crucial than application software. This is the reason why we should be concerned with the data quality for PaaS and IaaS because they handle data intensively. For this reason, we will apply the data quality model for PaaS and IaaS. In case of SaaS, it is enough to apply the product quality model without the data quality model. Figure 6 and 7 show the suggested application scope of the quality models of SaaS, PaaS and IaaS.
For Step 2, we define new quality sub-characteristics by analyzing the following aspects of cloud computing that are specified in the standards of SC38 (See Figure 8).
For example, one of the key characteristics of cloud computing is ‘measured service’ because CSC pays for cloud services based on how much they use resources through measured service. To provide measured service, the resource usage should be monitored, controlled, reported, and billed. To evaluate this feature, we suggest the measured services as the new sub-characteristics. services, the second step is the most important in defining a cloud quality model. For this reason, we need to conduct further studies on which kinds of quality sub-characteristics should be included in the quality model of cloud services by analyzing the key aspects of cloud computing.
In the previous chapter, we suggested the full set of quality sub-characteristics for CSP. In Step3, we classify the newly defined sub-characteristics into appropriate characteristics. If there is no appropriate characteristic, we propose the new one.
Figure 9 explains the key idea of sub-characteristics classification into the appropriate characteristics. After taking Step 3, we will have a quality model of cloud services provided by CSP. V.
CONCLUSION AND FUTURE WORK
The SQuaRE standards provide a basis for evaluating systems and software products. However, since it does not fit well with the new technology. For this reason, this paper proposed an approach to develop the quality model of cloud services.
In this paper, we proposed three steps to develop a quality model of cloud services. As the first step, we selected the appropriate quality sub-characteristics from the existing quality models with consideration of the characteristics of cloud services. The second step reflects the characteristics of cloud services into the quality model, so we suggested how to define new quality sub-characteristics for cloud computing. Last step classifies the quality sub-characteristics into characteristics. To apply the existing quality model to cloud —
Cloud [13] ISO/IEC 19944:2020 Cloud computing and distributed platforms ─ Data flow, data categories and data use — Part 1: Fundamentals