## 4 Proposed System Overview and Use of Open Link Data Integration for Polystore Databases
### Workflow Web-Based Query Management System with Top-Down Approach
#### 4.3.2 Proposal for Top-Down Polystore Systems Approach  
The bottom-up approach to creating a Polystore considers language translation as the main task, as shown in Figure 1. The existing datasets contain a large amount of data obtained from various data sources. There can be multiple languages to access these different datasets. The bottom-up approach is not preferred if a lot of data come from various sources and environments which support other languages and schemes. Thus, data and information in these kinds of the system create database connectivity issues or compatibility issues.  
The proposed system can support querying over multiple models uniformly and efficiently manage the information stored in various data models. For large and heterogeneous datasets such as ZTF, Polystores can provide top-down data management solutions. A framework for the top-down design process is shown in Figure 7. The activity begins with a requirement analysis that defines the system environment and data processing to create the database. For the data processing, we used two parallel activities: conceptual design and view design.  
Figure 8: Schema mapping architecture.  
Figure 7: Web Polystore System top-down design approach.  
The conceptual design stage is concerned with defining entity types and their connections. At the conceptual design stage, we select the ZTF catalog index file, the data in which should be stored in the database. These ZTF catalog index files were divided into separate entities, and the links between them were organized in the local RDBMS (Postgres). The database's fundamental entities are displayed as matrix tables in Table 4. The basic entities have different subclass, i.e., simple entity, complex entity, and N:N-link [49]. A simple entity is a collection of data about basic things recorded in a single database (for instance, HOST and FIELDS). A complex entity contains information on a complicated object that is logically maintained in several tables (for example, NIGHTS, FILTERS, FIELDS, CCD, and EXPOSURES). In a relational database, an N:N-link table is used to code N:N relationships (for example, HOST_FIELDS, EXPOSURE_CCD) where N:1 represents a many-to-one relationship and 1:N represents a one-to-many relationship. When expanding the conceptual model, the properties of each entity were determined and expanded as necessary by adding more indexes to the local catalogs.  
The view design activity is concerned with the definition of end-user interfaces. The proposed system enables users to access ZTF data via a graphical user interface (GUI) that includes an image visualizer, via simple and complicated queries from the PostgresQL database. The user has an option to select either science data product or reference data product by clicking on the sci or ref tab. The user interface of this system is created using HTML and CSS. JavaScript and PHP both offer dynamic and multistage table querying. Many systems can be extended from this architecture because more external views can be incorporated, and user workflow support can be added. The new additions or changes do not require query translation modifications. These only need to create dictionary entries at the conceptual level and support retrieval of these data items through an API at the data-server-side. The conceptual design might be understood as an integration of user perspectives. The activity of view integration is important since the conceptual design should accommodate both present and future applications [49]. The physical design links the conceptual schemas with real storage devices. At the physical design stage of this database, a data scheme physical model was constructed using the SQL relational database management system [50]. This database management system (DBMS) enables both basic and complicated query processing, with SQL created dynamically in response to user input with the graphical user interface (GUI). The generated query is then translated into predefined URL queries to the IPAC/IRSA web service in order to obtain the images.