## 6 Conclusions  
The preliminary estimation proposed in the current study is an integral part of the authors' estimation framework [9; 10]. According to the concept of the estimation life cycle (ELC), the preliminary estimation can be either the first stage or a logical continuation of the predecessor stage--the introductory estimation. In the second case, apart from an approximation of a timeline and budget, the introductory stage passes along the problem statement understanding, information about a business domain, and identified similar projects or products. Then, at the subsequent stage--the intermediate estimation--the inputs from the previous step are made more definitive by (a) reducing the number of project scenarios (ideally, to one main scenario); (b) detailing an EIBS; (c) adding specializations to a development team; and (d) splitting a project timeline into phases. The key advantage of the proposed preliminary estimation is that it belongs to the estimation framework covering the whole SDLC. Except for COCOO II [2], none of the existing methods is aimed at supporting the entire software project life cycle. Despite its high level of maturity, the main obstacle to using COCOO II is its complexity--preliminary estimation clearly has an advantage in this aspect. Use-case point analysis [17; 27; 28; 29; 30], which is also applicable in the early project stages, does not lose to the preliminary estimation regarding ease of use; however, in the authors' opinion, the formulas aimed at calculating use-case points and translating them to time-based units require a certain rethinking. Probably, an adjusted version of use-case point analysis might be a useful extension of the preliminary estimation sizing approach. The agile estimation methods [5; 6; 7; 8] are supposed to be applied rather at the implementation phase by an agile team when the project scope is decomposed to the user story level. Furthermore, those methods suffer from the lack of a tool set to translate story points to time-based units. Therefore, agile estimation methods (as they are originally defined) are hardly applicable at the early project stages. Similarity-based estimation [20; 21; 22; 23] can be either used in the introductory estimation stage or applied in conjunction with the preliminary estimation in order to verify the results. One of the most time-consuming and challenging parts of preliminary estimation is the project scope decomposition, i.e., building an EIBS. Usually, for this reason, an expert (a business analyst or a domain expert) has to process a large amount of information within a limited time frame. Some ideas on how to overcome such difficulties are given in Section 5. However, this matter is a separate topic that still requires further research. An important role that preliminary estimation plays is in the development working time coefficient (DWTC). Despite the considerations in Section 5, the recommendations on how to choose a DWTC value for a particular project are still not definitive enough. Obviously, the past project estimates are supposed to be used to define the coefficient's values. In the case of insufficiency of such historical data, DWTC values can rather be based on experts' judgment. To fully cover DWTC-related questions, further research is needed. From the practical implementation standpoint, preliminary estimation is a semistructured business process that, on the one hand, states what has to be done, and, on the other hand, intentionally leaves certain space for the involved experts' creativity. The proposed method of preliminary estimation is simple enough to be easily implemented with a spreadsheet like MS Excel or Google Spreadsheet.