Apps are software applications specifically designed for use on small, wireless computing devices, such as smartphones and tablets, and are not meant to be used on large, stationary computers such as desktops and laptops . A mobile application (mobile Apps) can be categorized by whether it is web-based or native, depending on whether it is explicitly designed for a given platform or created from the ground up for that platform. Another type of app is a hybrid app, which is a combination of native and web apps . It is critical to understand that functional and non-functional requirements (NFRs) play a crucial role in ensuring the product meets business requirements, such as speed, compatibility, localization, and capacity. According to [2] , the mobile application lifecycle consists of four phases as shown in Figure 1 . Each phase has several requirements, such as functional and non-functional requirements. Non-functional requirements (NFRs) play a crucial role in ensuring the success and satisfaction of mobile applications. These requirements go beyond the functionality of the app and focus on aspects such as usability, reliability, performance, and supportability. Understanding the consequences of analyzing functional and NFRs of mobile apps is essential for developers, designers, and stakeholders involved in mobile application development.

Hence, the purpose of this study is to analyse the four common NRFs of mobile Apps, which are usability, performance, reliability, and supportability, and to examine them in depth. The literature review method is used in this study. Thus, 27 mobile apps were collected and analysed based on the four NFRs of usability, performance, reliability, and supportability. Consequently, the authors found that 16 of the apps could meet the usability NFR, seven were able to meet the reliability NFR, fourteen covered the performance NFR, and three were able to meet the supportability NFR. At the same time, three were unable to meet any of the NFRs. According to the study results, mobile application developers place a greater emphasis on usability and performance than reliability and supportability in the development process. In contrast, a smaller percentage of developers prioritize reliability and supportability in their development process. The definitions of usability, performance, reliability, and supportability are as follows:

1) Usability: This refers to how easily and intuitively users can interact with the mobile application. It encompasses aspects such as ease of learning, efficiency of use, memorability, error prevention, and user satisfaction. A highly usable app is easy to navigate, understand, and use for its intended purpose.

2) Performance: This relates to the responsiveness, speed, and efficiency of the mobile application. It includes factors like loading times, processing speed, resource consumption (battery, memory), and the ability to handle a high volume of users or data without degradation in service.

3) Reliability: This concerns the ability of the mobile application to perform its intended functions consistently without failure. It involves aspects like stability, accuracy, fault tolerance, recoverability, and the ability to maintain performance under various conditions.

4) Supportability: This refers to how easily the mobile application can be maintained, updated, and adapted to changing requirements or technologies. It encompasses factors like maintainability, testability, scalability, portability, and the availability of documentation and support resources

This article is structured as follows: the related works are discussed in Section I, and the methodology is presented in Section III. The results and discussion are displayed in Section VI, whereas the conclusion and future work are discussed in Section V.

In the literature, there have been several models of mobile apps proposed for various purposes. The authors in [3] studied the usability of mobile applications within virtual environments based on several criteria, including the amount of time it took to complete the tasks, the number of errors the users made as well as the effectiveness and efficiency of their task completion. The authors in [4] conducted an empirical study, using a set of measures to assess the usability of mobile applications that are run on different mobile operating systems. A previous study, conducted by [5] , aimed to determine the most essential characteristics that define mobile applications, to facilitate the delivery of practical, outstanding, and user-friendly mobile apps that meet the needs of users. According to [6] , a systematic literature review was conducted to identify and collect the required evidence regarding the automated testing of mobile applications. Measuring the usability of a computer program requires considering three factors, namely effectiveness, efficiency, and satisfaction. The researchers at [7] designed a new usability model, namely, placing people at the centre of the mobile application development process. Additionally, they reviewed specific mobile applications to particular fields of study as well. Several mobile applications have been developed by the authors, including those that can be used to monitor the symptoms of heart failure [8] , cardiology , and diabetes [10] , among others, according to a study carried out by , seven different strategies can be used when estimating and selecting applications related to health.

Furthermore, mobile applications are employed in the education sector, especially for the purpose of teaching/learning language [11] [12] , m-learning [13] [14] . There are also smartphone applications that are used by undergraduate students [15] . Some applications exist for supporting the children suffering from autism spectrum disorders in a way to improve their capacities for understanding, interacting, and communicating with others with the use of the Arabic language [16] .

Some other researchers have examined the role mobile applications in tourism [17] [18] and spiritual/religious services [19] [20] . Nevertheless, the literature lacks the review of mobile applications in terms of their use in process related to pilgrimage. Furthermore, several scholars have designed different mobile applications applicable to various Hajj and Umrah services. Several master’s dissertations have been carried out on creating mobile applications that can guide Malaysian pilgrims [21] - [25] . In a masters’ thesis, proposed augmented reality aiming to guide pilgrims. In the studies of [27] , some mobile applications were designed, helping pilgrims to read Hajj and Umrah prayers and translating them into the pilgrims’ native language. A new framework was suggested by [28] , which serves as a crowd-sourcing platform defining the pilgrims’ needs. It employs mobile sensory data and, this way, defines the users’ contexts. The framework was employed for the development of a mobile application that could be used in numerous spatio-temporal services. In addition, [29] designed a mobile application serving as a dictionary for pilgrims who speak the Malay language. It has the capacity for translating three languages, i.e., Malay, Arabic, and English, to each other. The authors [30] suggested the utilization of a mobile phone for tracking purposes. This strategy could aid the guides (Mutawwif) of pilgrimage groups in recognizing their movements and determining their locations. A dynamic signage system was designed by [31] , which can be used as a mobile application that informs pilgrims regarding the crowd status around the Holy Ka’bah. Pilgrims can use this application to automatically count the number of Tawaf rounds performed. Another mobile application was designed by [32] , which is capable of guiding pilgrims when doing Umrah. It can also serve as Tawaf counter and location tracker. The authors in [33] introduced a service for identifying exact location in Hajj. It was able to gather information about the pilgrims’ locations to be used in identifying and tracking them. In another research, [34] offered a mobile translation application for the facilitation of communication among pilgrims. The advantage of this application is that it is accessible in numerous languages and uses technologies that recognize both text and voice to help pilgrims to correctly translate the target words. The “Al-Hajj” is a mobile application introduced by [35] , helping pilgrims understand Hajj-related deeds. It can exhibit four interactive features, i.e., map, checklist, motivational messages, and contact list. The authors [36] investigated how smartphone apps could be utilized to conduct surveys. They concentrated upon the collection of relevant data and information during mass gatherings. This can significantly enhance public health through the reinforcement of the knowledge associated with disease prevention. An analytical research was carried out by [37] into the mobile applications related to the Hajj practices, which are offered on Google Play. The applications identified in this regard were analysed with considering the following criteria: supported languages, offered services, installation rates, and repetition of the services and names of the applications. The authors [38] developed an integrated classified model that illustrates mobile app usability from the high-ranking stage of “usability standards” to the middle level of “usability elements” to the comprehensive level of “usability elements” to evaluate the usability of present mobile apps from diverse classifications. [39] investigated the quality aspects that inspire students and lecturers’ usage of the Elearning. ZUJ mobile application at the Al-Zaytoonah University of Jordan. Additionally, the research revealed how well the quality aspects fit the desires of students and lecturers who applied the application during the academic year 2020 - 2021. The authors in [40] applied the fuzzy TOPSIS method to choose high-value and user skills of mobile education products for mathematics. They recognized the issues that are damaging the use of mobile mathematics education applications and proposed solutions to deal with such issues. The authors in [41] investigated how gamification may encourage user action and encouraging marketing results. They supplied several abstract and functional effects that can assist designers create more efficient gamified mobile apps. The authors in [42] identified stakeholder opinions on essential conditions for introducing mobile health schemes and appropriate consequences regarding reasonable and cost usefulness of effective mobile health schemes. The authors in [43] proposed and evaluated a novel hybrid model to examine the behavioural aims of young customers to utilize mobile apps. The authors in [44] introduced an emergency model of operating factors of consumer appointment in the context of selling mobile apps. The proposed model improved the existing literature of consumer commitment management that has been getting power lately within the field of online benefit study. The researchers in [45] introduced usability research that seeks to create a consistent, flexible, complete scale for categorization and measuring the features of health products.

On the other hand, several studies have discussed cybercrime, which may affect the privacy and security of the data in the mobile apps and their database [46] - [67] .

Existing literature features a wide range of mobile apps for purposes like healthcare, education, tourism, and religious services. Research has examined usability models, automated testing methods, and domain-specific frameworks such as language learning and Hajj pilgrimage. However, there is a notable gap in the comprehensive review of these applications’ non-functional requirements (NFRs), especially regarding usability, reliability, performance, and supportability, along with some analysis of the related studies’ work. This paper addresses this gap by analyzing the NFRs across various mobile applications and industries. By emphasizing these critical quality attributes, the study aims to provide valuable insights for developers, designers, and stakeholders, fostering the development of more robust, user-friendly, and maintainable applications.

To accomplish this objective, this study uses the literature review method [68] to go through all the different resources and collect and discover the mobile apps. In order to gather mobile app articles from different resources, five search engines have been identified in order to gather the articles. There are three keywords used in this study: “Mobile Apps”, “Mobile Applications” and “non-functional requirements”. The searching period identified from 2015 - 2024. Also, the inclusion and exclusion criteria are identified and listed as shown in Table 1 . Then, based on the identified search rules, the data was gathered from the common search engines via the identified search engines. Based on the results of the search engines, there were 2091 articles found. Based on the criteria listed in Table 1 , the 2091 articles gathered are filtered based on the inclusion and exclusion criteria, and then 27 articles for this study have been selected based on those criteria as shown in Table 2 . Figure 2 displays the methodology used.

According to this analysis, most of the mobile Apps developers focused on the usability, performance, and reliability NFRs, while the supportability NFR were the less used by the mobile Apps developers in their development process. The usability NFR refers to how easy and intuitive a mobile App is to use. Developers prioritize this NFR to ensure that users can easily navigate through the mobile app, find the information they need, and complete the desired tasks. By focusing on usability, developers aim to create a seamless and enjoyable user experience. Performance is another critical NFR that mobile developers consider. They ensure that a mobile apps responds quickly, loads data efficiently, and runs smoothly on different devices and network conditions. By optimizing the app’s performance, developers aim to maintain a smooth and responsive user experience, regardless of external factors. Reliability is another crucial NFR that mobile developers prioritize. They ensure that a mobile apps consistently delivers the expected results and does not experience crashes or errors. By thoroughly testing the app and implementing robust error handling mechanisms, developers aim to maintain a high level of reliability, ensuring users trust the App and rely on it for their daily tasks. In contrast, supportability was found to be the less used NFR in the mobile apps development process. Supportability refers to how easily a mobile apps can be maintained, updated, and integrated with other systems. While developers understand the importance of supportability, they may focus more on the immediate needs of a mobile app’s functionality rather than long-term maintenance.

Thus, most of the mobile apps developers emphasized usability, performance, and reliability as key NFRs during development. While supportability was considered important, it was generally less prioritized compared to the NFRs, likely due to its focus on long-term maintenance and integration.

In contrast, the 27 mobile apps that were included in the survey covered a variety of industries. There were some of these models that dealt with the health sector, some that dealt with the education sector, and so on. Table 3 displays the outcome, methodology and variety of industries which covered by the 27 mobile apps. Furthermore, each mobile apps of the 27 has advantages and disadvantages as shown in Table 4 .

The purpose of this section is to provide a deep discussion and analysis of the study. Developing a mobile app is a crucial stage that requires empirical research to determine the development requirements. During the study, 27 mobile apps derived from such NFRs were collected and analyzed. Based on the results of the study, some of these apps covered whole NRFs, some covered partial NRFs, and some didn’t cover any NRFs at all. As a result of the study, most of the mobile apps analyzed were focused primarily on usability and performance requirements. Figure 4 shows the diversity of the coverage provided by 27 mobile apps for the NRFs.

Figure 4 shows that the developers of the mobile app focused primarily on the usability requirements and subsequently on performance requirements when it came to developing the mobile app. This decision was driven by a strong motivation, which was the need to develop an app that would be user-friendly and efficient, that would improve user satisfaction, increase user retention, optimize performance, and gain a competitive edge in the market. App development can be very successful when developers pay equal attention to usability and performance. By doing so, they can create an app that meets their users’ expectations and remains relevant. This is in a market where mobile apps are constantly changing to remain relevant.

Nevertheless, most of the developers, as well as the majority of the authors, have not addressed the supportability requirement sufficiently, and only three of them have done so. It appears that this crucial component was ignored or neglected during the development process, which suggests that they overlooked or neglected it. In this case, it means that little attention was given to the requirements for the product’s supportability, which means that nothing was done to ensure the product’s long-term viability or to ensure that it can be maintained over time. Supportability is a crucial component of maintaining and updating software systems, and if this aspect is overlooked, there could be significant consequences for the product's stability and usability. Supportability must be prioritized and understood by developers as a key factor for ensuring the successful implementation of a product and its continued maintenance over the long term.

Functional requirements define what a mobile application does-the specific features and functionalities it offers to the user. These are typically described in terms of actions the system should perform, such as user login, data input, transaction processing, or information retrieval. Functional requirements are often the initial focus of development, as they form the core value proposition of the App. Without robust functional features, the App can’t deliver on its intended purpose, regardless of its performance or usability. Therefore, developers often prioritize the implementation of these features to establish a working product as quickly as possible.

However, non-functional requirements (NFRs) determine how well the App performs these functions. They include qualities such as usability, reliability, performance, security, and supportability. While the App might technically fulfill what it’s supposed to do (meeting the functional requirements), poor NFRs can significantly harm the user experience and ultimately harm the App’s success. For example, an e-commerce app with a detailed product catalog (functional) but slow loading times and frequent crashes (poor NFRs) will likely frustrate users and result in low conversion rates. Ignoring NFRs and focusing only on functional features is a common mistake that can lead to a technically correct but practically unusable or unsustainable application.

Ultimately, a successful mobile app requires a careful balance between functional and non-functional requirements. While functional requirements define the App’s core capabilities, NFRs determine its overall quality, user satisfaction, and long-term viability. Ideally, development teams should consider both aspects simultaneously, refining both the features and qualities of the App throughout the development process. Focusing on only one at the expense of the other can result in a subpar product that does not meet user expectations or achieve its goals. This integrated approach ensures that the App is not only functional but also enjoyable, reliable, and easy to maintain. Table 5 NFR Prioritization and Potential Driving Factors.

A variety of mobile apps are used every day by most people, including news apps, social media apps, and shopping apps. To ensure their reliability when used in the field, these mobile apps must be thoroughly tested. Usually, manual testing for mobile apps is extremely cost-prohibitive because it involves human effort in defining tests and checking results, which can take a considerable amount of time. Developers must therefore conduct empirical studies on how nonfunctional requirements are treated by developers in mobile app development, and how they compare to functional requirements. According to this study, we examined the non-functional requirements (NFRs) of mobile apps from four perspectives: the usability of the mobile App, its reliability, its performance, and even its supportability. A survey of 27 mobile applications collected revealed that 16 out of 27 covered the usability NFR, 7 out of 27 covered the reliability NFR, 14 out of 27 covered the performance NFRs, and 3 out of 27 covered supportability NFRs; however, three out of 27 mobile apps did not meet any of the NFR criteria. As a result of this study, it has been discovered that mobile app developers focus primarily on usability and performance, while reliability and supportability are less deeply integrated into the process of developing apps for mobile devices. In the future work of this study, we will be analyzing mobile applications from the functional requirements and comparing them with our results, as well as developing a comprehensive framework that incorporates full functional requirements and non-functional requirements into a single framework that can be applied to mobile applications. Additionally, the primary study should include efforts to capture the latest trends and advancements in mobile app development.