• Global close

**Datasets of opinion polls and surveys** are the largest and most frequently used collection of data by users from social science community. The largest part of this collection consists of data from surveys carried out by other scientists and researchers, which might be used by other users for their own **secondary analysis**. Launched in 2006 the LiDA Survey Data collection currently contains **more than 300 survey datasets** (not all datasets are available yet, as a migration project from the old infrastructure is underway for the period 2020-2024). The datasets are organised into **thematic collections** – sub-catalogues. Each survey dataset is described (documented) in **English** (see Metadata: Citation Metadata, Geospatial Metadata, Social Science and Humanities Metadata) and **Lithuanian** (see Metadata: Citation Metadata (LT), Geospatial Metadata (LT), Social Science and Humanities Metadata (LT)).

The set of datasets, methods, applications and experiments developed by the SoBigData community.

BASE is one of the world's most voluminous search engines especially for scholarly web resources. BASE offers more than 314 million documents from more than 10,000 content providers. The full texts of about 60% of the indexed documents are accessible free of charge (Open Access). BASE is operated by Bielefeld University Library. BASE index the metadata of all types of scholarly resources – journals, institutional repositories, digital collections, etc. – that have an OAI interface and use OAI-PMH to make their metadata available (see our Golden Rules for Repository Managers). The index will be continuously expanded by integrating further sources / content provider (Become a content provider). We are working on several new features such as a ORCID claiming service for authors. BASE is a registered OAI service provider. Database managers can integrate the BASE index into their local infrastructure (e.g. metasearch engines, library catalogues). In addition, there are various tools and services for users, database and repository managers. Compared to commercial search engines, BASE is charcterised by the following features: - Content providers are indexed only after being checked by qualified staff of Bielefeld University Library. - Only document servers and journals that meet specific requirements for academic quality and relevance are included. - Our list of content providers ensures transparency in searching. - Web resources of the "Deep Web" are indexed which are ignored by commercial search engines or are lost in the mass of hits. - Correction, normalisation and enrichment of metadata are supported by automated methods. - Mulitlingual search (find search terms in more than 20 translated languages). - The display of search results includes accurate bibliographic data. - Display of access type (Open Access) and license conditions for a publication. - Multiple options for sorting the results list (by author, title, date). - Refinement of search results (by author, subject, DDC, year of publication, content provider, language, document type, access type and license terms) - Browsing by DDC (Dewey Decimal Classification), document type, access type and license terms.